deparse.c

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/*-------------------------------------------------------------------------
 *
 * deparse.c
 *        Query deparser for postgres_fdw
 *
 * This file includes functions that examine query WHERE clauses to see
 * whether they're safe to send to the remote server for execution, as
 * well as functions to construct the query text to be sent.  The latter
 * functionality is annoyingly duplicative of ruleutils.c, but there are
 * enough special considerations that it seems best to keep this separate.
 * One saving grace is that we only need deparse logic for node types that
 * we consider safe to send.
 *
 * We assume that the remote session's search_path is exactly "pg_catalog",
 * and thus we need schema-qualify all and only names outside pg_catalog.
 *
 * We do not consider that it is ever safe to send COLLATE expressions to
 * the remote server: it might not have the same collation names we do.
 * (Later we might consider it safe to send COLLATE "C", but even that would
 * fail on old remote servers.)  An expression is considered safe to send
 * only if all operator/function input collations used in it are traceable to
 * Var(s) of the foreign table.  That implies that if the remote server gets
 * a different answer than we do, the foreign table's columns are not marked
 * with collations that match the remote table's columns, which we can
 * consider to be user error.
 *
 * Portions Copyright (c) 2012-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *        contrib/postgres_fdw/deparse.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/htup_details.h"
#include "access/sysattr.h"
#include "access/table.h"
#include "catalog/pg_aggregate.h"
#include "catalog/pg_authid.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_opfamily.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_ts_config.h"
#include "catalog/pg_ts_dict.h"
#include "catalog/pg_type.h"
#include "commands/defrem.h"
#include "nodes/nodeFuncs.h"
#include "nodes/plannodes.h"
#include "optimizer/optimizer.h"
#include "optimizer/prep.h"
#include "optimizer/tlist.h"
#include "parser/parsetree.h"
#include "postgres_fdw.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/syscache.h"
#include "utils/typcache.h"
 
/*
 * Global context for foreign_expr_walker's search of an expression tree.
 */
typedef struct foreign_glob_cxt
{
    PlannerInfo *root;          /* global planner state */
    RelOptInfo *foreignrel;     /* the foreign relation we are planning for */
    Relids      relids;         /* relids of base relations in the underlying
                                 * scan */
} foreign_glob_cxt;
 
/*
 * Local (per-tree-level) context for foreign_expr_walker's search.
 * This is concerned with identifying collations used in the expression.
 */
typedef enum
{
    FDW_COLLATE_NONE,           /* expression is of a noncollatable type, or
                                 * it has default collation that is not
                                 * traceable to a foreign Var */
    FDW_COLLATE_SAFE,           /* collation derives from a foreign Var */
    FDW_COLLATE_UNSAFE,         /* collation is non-default and derives from
                                 * something other than a foreign Var */
} FDWCollateState;
 
typedef struct foreign_loc_cxt
{
    Oid         collation;      /* OID of current collation, if any */
    FDWCollateState state;      /* state of current collation choice */
} foreign_loc_cxt;
 
/*
 * Context for deparseExpr
 */
typedef struct deparse_expr_cxt
{
    PlannerInfo *root;          /* global planner state */
    RelOptInfo *foreignrel;     /* the foreign relation we are planning for */
    RelOptInfo *scanrel;        /* the underlying scan relation. Same as
                                 * foreignrel, when that represents a join or
                                 * a base relation. */
    StringInfo  buf;            /* output buffer to append to */
    List      **params_list;    /* exprs that will become remote Params */
} deparse_expr_cxt;
 
#define REL_ALIAS_PREFIX    "r"
/* Handy macro to add relation name qualification */
#define ADD_REL_QUALIFIER(buf, varno)   \
        appendStringInfo((buf), "%s%d.", REL_ALIAS_PREFIX, (varno))
#define SUBQUERY_REL_ALIAS_PREFIX   "s"
#define SUBQUERY_COL_ALIAS_PREFIX   "c"
 
/*
 * Functions to determine whether an expression can be evaluated safely on
 * remote server.
 */
static bool foreign_expr_walker(Node *node,
                                foreign_glob_cxt *glob_cxt,
                                foreign_loc_cxt *outer_cxt,
                                foreign_loc_cxt *case_arg_cxt);
static char *deparse_type_name(Oid type_oid, int32 typemod);
 
/*
 * Functions to construct string representation of a node tree.
 */
static void deparseTargetList(StringInfo buf,
                              RangeTblEntry *rte,
                              Index rtindex,
                              Relation rel,
                              bool is_returning,
                              Bitmapset *attrs_used,
                              bool qualify_col,
                              List **retrieved_attrs);
static void deparseExplicitTargetList(List *tlist,
                                      bool is_returning,
                                      List **retrieved_attrs,
                                      deparse_expr_cxt *context);
static void deparseSubqueryTargetList(deparse_expr_cxt *context);
static void deparseReturningList(StringInfo buf, RangeTblEntry *rte,
                                 Index rtindex, Relation rel,
                                 bool trig_after_row,
                                 List *withCheckOptionList,
                                 List *returningList,
                                 List **retrieved_attrs);
static void deparseColumnRef(StringInfo buf, int varno, int varattno,
                             RangeTblEntry *rte, bool qualify_col);
static void deparseRelation(StringInfo buf, Relation rel);
static void deparseExpr(Expr *node, deparse_expr_cxt *context);
static void deparseVar(Var *node, deparse_expr_cxt *context);
static void deparseConst(Const *node, deparse_expr_cxt *context, int showtype);
static void deparseParam(Param *node, deparse_expr_cxt *context);
static void deparseSubscriptingRef(SubscriptingRef *node, deparse_expr_cxt *context);
static void deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context);
static void deparseOpExpr(OpExpr *node, deparse_expr_cxt *context);
static bool isPlainForeignVar(Expr *node, deparse_expr_cxt *context);
static void deparseOperatorName(StringInfo buf, Form_pg_operator opform);
static void deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context);
static void deparseScalarArrayOpExpr(ScalarArrayOpExpr *node,
                                     deparse_expr_cxt *context);
static void deparseRelabelType(RelabelType *node, deparse_expr_cxt *context);
static void deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context);
static void deparseNullTest(NullTest *node, deparse_expr_cxt *context);
static void deparseCaseExpr(CaseExpr *node, deparse_expr_cxt *context);
static void deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context);
static void printRemoteParam(int paramindex, Oid paramtype, int32 paramtypmod,
                             deparse_expr_cxt *context);
static void printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
                                   deparse_expr_cxt *context);
static void deparseSelectSql(List *tlist, bool is_subquery, List **retrieved_attrs,
                             deparse_expr_cxt *context);
static void deparseLockingClause(deparse_expr_cxt *context);
static void appendOrderByClause(List *pathkeys, bool has_final_sort,
                                deparse_expr_cxt *context);
static void appendLimitClause(deparse_expr_cxt *context);
static void appendConditions(List *exprs, deparse_expr_cxt *context);
static void deparseFromExprForRel(StringInfo buf, PlannerInfo *root,
                                  RelOptInfo *foreignrel, bool use_alias,
                                  Index ignore_rel, List **ignore_conds,
                                  List **additional_conds,
                                  List **params_list);
static void appendWhereClause(List *exprs, List *additional_conds,
                              deparse_expr_cxt *context);
static void deparseFromExpr(List *quals, deparse_expr_cxt *context);
static void deparseRangeTblRef(StringInfo buf, PlannerInfo *root,
                               RelOptInfo *foreignrel, bool make_subquery,
                               Index ignore_rel, List **ignore_conds,
                               List **additional_conds, List **params_list);
static void deparseAggref(Aggref *node, deparse_expr_cxt *context);
static void appendGroupByClause(List *tlist, deparse_expr_cxt *context);
static void appendOrderBySuffix(Oid sortop, Oid sortcoltype, bool nulls_first,
                                deparse_expr_cxt *context);
static void appendAggOrderBy(List *orderList, List *targetList,
                             deparse_expr_cxt *context);
static void appendFunctionName(Oid funcid, deparse_expr_cxt *context);
static Node *deparseSortGroupClause(Index ref, List *tlist, bool force_colno,
                                    deparse_expr_cxt *context);
 
/*
 * Helper functions
 */
static bool is_subquery_var(Var *node, RelOptInfo *foreignrel,
                            int *relno, int *colno);
static void get_relation_column_alias_ids(Var *node, RelOptInfo *foreignrel,
                                          int *relno, int *colno);
 
 
/*
 * Examine each qual clause in input_conds, and classify them into two groups,
 * which are returned as two lists:
 *  - remote_conds contains expressions that can be evaluated remotely
 *  - local_conds contains expressions that can't be evaluated remotely
 */
void
classifyConditions(PlannerInfo *root,
                   RelOptInfo *baserel,
                   List *input_conds,
                   List **remote_conds,
                   List **local_conds)
{
    ListCell   *lc;
 
    *remote_conds = NIL;
    *local_conds = NIL;
 
    foreach(lc, input_conds)
    {
        RestrictInfo *ri = lfirst_node(RestrictInfo, lc);
 
        if (is_foreign_expr(root, baserel, ri->clause))
            *remote_conds = lappend(*remote_conds, ri);
        else
            *local_conds = lappend(*local_conds, ri);
    }
}
 
/*
 * Returns true if given expr is safe to evaluate on the foreign server.
 */
bool
is_foreign_expr(PlannerInfo *root,
                RelOptInfo *baserel,
                Expr *expr)
{
    foreign_glob_cxt glob_cxt;
    foreign_loc_cxt loc_cxt;
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) (baserel->fdw_private);
 
    /*
     * Check that the expression consists of nodes that are safe to execute
     * remotely.
     */
    glob_cxt.root = root;
    glob_cxt.foreignrel = baserel;
 
    /*
     * For an upper relation, use relids from its underneath scan relation,
     * because the upperrel's own relids currently aren't set to anything
     * meaningful by the core code.  For other relation, use their own relids.
     */
    if (IS_UPPER_REL(baserel))
        glob_cxt.relids = fpinfo->outerrel->relids;
    else
        glob_cxt.relids = baserel->relids;
    loc_cxt.collation = InvalidOid;
    loc_cxt.state = FDW_COLLATE_NONE;
    if (!foreign_expr_walker((Node *) expr, &glob_cxt, &loc_cxt, NULL))
        return false;
 
    /*
     * If the expression has a valid collation that does not arise from a
     * foreign var, the expression can not be sent over.
     */
    if (loc_cxt.state == FDW_COLLATE_UNSAFE)
        return false;
 
    /*
     * An expression which includes any mutable functions can't be sent over
     * because its result is not stable.  For example, sending now() remote
     * side could cause confusion from clock offsets.  Future versions might
     * be able to make this choice with more granularity.  (We check this last
     * because it requires a lot of expensive catalog lookups.)
     */
    if (contain_mutable_functions((Node *) expr))
        return false;
 
    /* OK to evaluate on the remote server */
    return true;
}
 
/*
 * Check if expression is safe to execute remotely, and return true if so.
 *
 * In addition, *outer_cxt is updated with collation information.
 *
 * case_arg_cxt is NULL if this subexpression is not inside a CASE-with-arg.
 * Otherwise, it points to the collation info derived from the arg expression,
 * which must be consulted by any CaseTestExpr.
 *
 * We must check that the expression contains only node types we can deparse,
 * that all types/functions/operators are safe to send (they are "shippable"),
 * and that all collations used in the expression derive from Vars of the
 * foreign table.  Because of the latter, the logic is pretty close to
 * assign_collations_walker() in parse_collate.c, though we can assume here
 * that the given expression is valid.  Note function mutability is not
 * currently considered here.
 */
static bool
foreign_expr_walker(Node *node,
                    foreign_glob_cxt *glob_cxt,
                    foreign_loc_cxt *outer_cxt,
                    foreign_loc_cxt *case_arg_cxt)
{
    bool        check_type = true;
    PgFdwRelationInfo *fpinfo;
    foreign_loc_cxt inner_cxt;
    Oid         collation;
    FDWCollateState state;
 
    /* Need do nothing for empty subexpressions */
    if (node == NULL)
        return true;
 
    /* May need server info from baserel's fdw_private struct */
    fpinfo = (PgFdwRelationInfo *) (glob_cxt->foreignrel->fdw_private);
 
    /* Set up inner_cxt for possible recursion to child nodes */
    inner_cxt.collation = InvalidOid;
    inner_cxt.state = FDW_COLLATE_NONE;
 
    switch (nodeTag(node))
    {
        case T_Var:
            {
                Var        *var = (Var *) node;
 
                /*
                 * If the Var is from the foreign table, we consider its
                 * collation (if any) safe to use.  If it is from another
                 * table, we treat its collation the same way as we would a
                 * Param's collation, ie it's not safe for it to have a
                 * non-default collation.
                 */
                if (bms_is_member(var->varno, glob_cxt->relids) &&
                    var->varlevelsup == 0)
                {
                    /* Var belongs to foreign table */
 
                    /*
                     * System columns other than ctid should not be sent to
                     * the remote, since we don't make any effort to ensure
                     * that local and remote values match (tableoid, in
                     * particular, almost certainly doesn't match).
                     */
                    if (var->varattno < 0 &&
                        var->varattno != SelfItemPointerAttributeNumber)
                        return false;
 
                    /* Else check the collation */
                    collation = var->varcollid;
                    state = OidIsValid(collation) ? FDW_COLLATE_SAFE : FDW_COLLATE_NONE;
                }
                else
                {
                    /* Var belongs to some other table */
                    collation = var->varcollid;
                    if (collation == InvalidOid ||
                        collation == DEFAULT_COLLATION_OID)
                    {
                        /*
                         * It's noncollatable, or it's safe to combine with a
                         * collatable foreign Var, so set state to NONE.
                         */
                        state = FDW_COLLATE_NONE;
                    }
                    else
                    {
                        /*
                         * Do not fail right away, since the Var might appear
                         * in a collation-insensitive context.
                         */
                        state = FDW_COLLATE_UNSAFE;
                    }
                }
            }
            break;
        case T_Const:
            {
                Const      *c = (Const *) node;
 
                /*
                 * Constants of regproc and related types can't be shipped
                 * unless the referenced object is shippable.  But NULL's ok.
                 * (See also the related code in dependency.c.)
                 */
                if (!c->constisnull)
                {
                    switch (c->consttype)
                    {
                        case REGPROCOID:
                        case REGPROCEDUREOID:
                            if (!is_shippable(DatumGetObjectId(c->constvalue),
                                              ProcedureRelationId, fpinfo))
                                return false;
                            break;
                        case REGOPEROID:
                        case REGOPERATOROID:
                            if (!is_shippable(DatumGetObjectId(c->constvalue),
                                              OperatorRelationId, fpinfo))
                                return false;
                            break;
                        case REGCLASSOID:
                            if (!is_shippable(DatumGetObjectId(c->constvalue),
                                              RelationRelationId, fpinfo))
                                return false;
                            break;
                        case REGTYPEOID:
                            if (!is_shippable(DatumGetObjectId(c->constvalue),
                                              TypeRelationId, fpinfo))
                                return false;
                            break;
                        case REGCOLLATIONOID:
                            if (!is_shippable(DatumGetObjectId(c->constvalue),
                                              CollationRelationId, fpinfo))
                                return false;
                            break;
                        case REGCONFIGOID:
 
                            /*
                             * For text search objects only, we weaken the
                             * normal shippability criterion to allow all OIDs
                             * below FirstNormalObjectId.  Without this, none
                             * of the initdb-installed TS configurations would
                             * be shippable, which would be quite annoying.
                             */
                            if (DatumGetObjectId(c->constvalue) >= FirstNormalObjectId &&
                                !is_shippable(DatumGetObjectId(c->constvalue),
                                              TSConfigRelationId, fpinfo))
                                return false;
                            break;
                        case REGDICTIONARYOID:
                            if (DatumGetObjectId(c->constvalue) >= FirstNormalObjectId &&
                                !is_shippable(DatumGetObjectId(c->constvalue),
                                              TSDictionaryRelationId, fpinfo))
                                return false;
                            break;
                        case REGNAMESPACEOID:
                            if (!is_shippable(DatumGetObjectId(c->constvalue),
                                              NamespaceRelationId, fpinfo))
                                return false;
                            break;
                        case REGROLEOID:
                            if (!is_shippable(DatumGetObjectId(c->constvalue),
                                              AuthIdRelationId, fpinfo))
                                return false;
                            break;
                    }
                }
 
                /*
                 * If the constant has nondefault collation, either it's of a
                 * non-builtin type, or it reflects folding of a CollateExpr.
                 * It's unsafe to send to the remote unless it's used in a
                 * non-collation-sensitive context.
                 */
                collation = c->constcollid;
                if (collation == InvalidOid ||
                    collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_Param:
            {
                Param      *p = (Param *) node;
 
                /*
                 * If it's a MULTIEXPR Param, punt.  We can't tell from here
                 * whether the referenced sublink/subplan contains any remote
                 * Vars; if it does, handling that is too complicated to
                 * consider supporting at present.  Fortunately, MULTIEXPR
                 * Params are not reduced to plain PARAM_EXEC until the end of
                 * planning, so we can easily detect this case.  (Normal
                 * PARAM_EXEC Params are safe to ship because their values
                 * come from somewhere else in the plan tree; but a MULTIEXPR
                 * references a sub-select elsewhere in the same targetlist,
                 * so we'd be on the hook to evaluate it somehow if we wanted
                 * to handle such cases as direct foreign updates.)
                 */
                if (p->paramkind == PARAM_MULTIEXPR)
                    return false;
 
                /*
                 * Collation rule is same as for Consts and non-foreign Vars.
                 */
                collation = p->paramcollid;
                if (collation == InvalidOid ||
                    collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_SubscriptingRef:
            {
                SubscriptingRef *sr = (SubscriptingRef *) node;
 
                /* Assignment should not be in restrictions. */
                if (sr->refassgnexpr != NULL)
                    return false;
 
                /*
                 * Recurse into the remaining subexpressions.  The container
                 * subscripts will not affect collation of the SubscriptingRef
                 * result, so do those first and reset inner_cxt afterwards.
                 */
                if (!foreign_expr_walker((Node *) sr->refupperindexpr,
                                         glob_cxt, &inner_cxt, case_arg_cxt))
                    return false;
                inner_cxt.collation = InvalidOid;
                inner_cxt.state = FDW_COLLATE_NONE;
                if (!foreign_expr_walker((Node *) sr->reflowerindexpr,
                                         glob_cxt, &inner_cxt, case_arg_cxt))
                    return false;
                inner_cxt.collation = InvalidOid;
                inner_cxt.state = FDW_COLLATE_NONE;
                if (!foreign_expr_walker((Node *) sr->refexpr,
                                         glob_cxt, &inner_cxt, case_arg_cxt))
                    return false;
 
                /*
                 * Container subscripting typically yields same collation as
                 * refexpr's, but in case it doesn't, use same logic as for
                 * function nodes.
                 */
                collation = sr->refcollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_FuncExpr:
            {
                FuncExpr   *fe = (FuncExpr *) node;
 
                /*
                 * If function used by the expression is not shippable, it
                 * can't be sent to remote because it might have incompatible
                 * semantics on remote side.
                 */
                if (!is_shippable(fe->funcid, ProcedureRelationId, fpinfo))
                    return false;
 
                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) fe->args,
                                         glob_cxt, &inner_cxt, case_arg_cxt))
                    return false;
 
                /*
                 * If function's input collation is not derived from a foreign
                 * Var, it can't be sent to remote.
                 */
                if (fe->inputcollid == InvalidOid)
                     /* OK, inputs are all noncollatable */ ;
                else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                         fe->inputcollid != inner_cxt.collation)
                    return false;
 
                /*
                 * Detect whether node is introducing a collation not derived
                 * from a foreign Var.  (If so, we just mark it unsafe for now
                 * rather than immediately returning false, since the parent
                 * node might not care.)
                 */
                collation = fe->funccollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_OpExpr:
        case T_DistinctExpr:    /* struct-equivalent to OpExpr */
            {
                OpExpr     *oe = (OpExpr *) node;
 
                /*
                 * Similarly, only shippable operators can be sent to remote.
                 * (If the operator is shippable, we assume its underlying
                 * function is too.)
                 */
                if (!is_shippable(oe->opno, OperatorRelationId, fpinfo))
                    return false;
 
                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) oe->args,
                                         glob_cxt, &inner_cxt, case_arg_cxt))
                    return false;
 
                /*
                 * If operator's input collation is not derived from a foreign
                 * Var, it can't be sent to remote.
                 */
                if (oe->inputcollid == InvalidOid)
                     /* OK, inputs are all noncollatable */ ;
                else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                         oe->inputcollid != inner_cxt.collation)
                    return false;
 
                /* Result-collation handling is same as for functions */
                collation = oe->opcollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_ScalarArrayOpExpr:
            {
                ScalarArrayOpExpr *oe = (ScalarArrayOpExpr *) node;
 
                /*
                 * Again, only shippable operators can be sent to remote.
                 */
                if (!is_shippable(oe->opno, OperatorRelationId, fpinfo))
                    return false;
 
                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) oe->args,
                                         glob_cxt, &inner_cxt, case_arg_cxt))
                    return false;
 
                /*
                 * If operator's input collation is not derived from a foreign
                 * Var, it can't be sent to remote.
                 */
                if (oe->inputcollid == InvalidOid)
                     /* OK, inputs are all noncollatable */ ;
                else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                         oe->inputcollid != inner_cxt.collation)
                    return false;
 
                /* Output is always boolean and so noncollatable. */
                collation = InvalidOid;
                state = FDW_COLLATE_NONE;
            }
            break;
        case T_RelabelType:
            {
                RelabelType *r = (RelabelType *) node;
 
                /*
                 * Recurse to input subexpression.
                 */
                if (!foreign_expr_walker((Node *) r->arg,
                                         glob_cxt, &inner_cxt, case_arg_cxt))
                    return false;
 
                /*
                 * RelabelType must not introduce a collation not derived from
                 * an input foreign Var (same logic as for a real function).
                 */
                collation = r->resultcollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_BoolExpr:
            {
                BoolExpr   *b = (BoolExpr *) node;
 
                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) b->args,
                                         glob_cxt, &inner_cxt, case_arg_cxt))
                    return false;
 
                /* Output is always boolean and so noncollatable. */
                collation = InvalidOid;
                state = FDW_COLLATE_NONE;
            }
            break;
        case T_NullTest:
            {
                NullTest   *nt = (NullTest *) node;
 
                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) nt->arg,
                                         glob_cxt, &inner_cxt, case_arg_cxt))
                    return false;
 
                /* Output is always boolean and so noncollatable. */
                collation = InvalidOid;
                state = FDW_COLLATE_NONE;
            }
            break;
        case T_CaseExpr:
            {
                CaseExpr   *ce = (CaseExpr *) node;
                foreign_loc_cxt arg_cxt;
                foreign_loc_cxt tmp_cxt;
                ListCell   *lc;
 
                /*
                 * Recurse to CASE's arg expression, if any.  Its collation
                 * has to be saved aside for use while examining CaseTestExprs
                 * within the WHEN expressions.
                 */
                arg_cxt.collation = InvalidOid;
                arg_cxt.state = FDW_COLLATE_NONE;
                if (ce->arg)
                {
                    if (!foreign_expr_walker((Node *) ce->arg,
                                             glob_cxt, &arg_cxt, case_arg_cxt))
                        return false;
                }
 
                /* Examine the CaseWhen subexpressions. */
                foreach(lc, ce->args)
                {
                    CaseWhen   *cw = lfirst_node(CaseWhen, lc);
 
                    if (ce->arg)
                    {
                        /*
                         * In a CASE-with-arg, the parser should have produced
                         * WHEN clauses of the form "CaseTestExpr = RHS",
                         * possibly with an implicit coercion inserted above
                         * the CaseTestExpr.  However in an expression that's
                         * been through the optimizer, the WHEN clause could
                         * be almost anything (since the equality operator
                         * could have been expanded into an inline function).
                         * In such cases forbid pushdown, because
                         * deparseCaseExpr can't handle it.
                         */
                        Node       *whenExpr = (Node *) cw->expr;
                        List       *opArgs;
 
                        if (!IsA(whenExpr, OpExpr))
                            return false;
 
                        opArgs = ((OpExpr *) whenExpr)->args;
                        if (list_length(opArgs) != 2 ||
                            !IsA(strip_implicit_coercions(linitial(opArgs)),
                                 CaseTestExpr))
                            return false;
                    }
 
                    /*
                     * Recurse to WHEN expression, passing down the arg info.
                     * Its collation doesn't affect the result (really, it
                     * should be boolean and thus not have a collation).
                     */
                    tmp_cxt.collation = InvalidOid;
                    tmp_cxt.state = FDW_COLLATE_NONE;
                    if (!foreign_expr_walker((Node *) cw->expr,
                                             glob_cxt, &tmp_cxt, &arg_cxt))
                        return false;
 
                    /* Recurse to THEN expression. */
                    if (!foreign_expr_walker((Node *) cw->result,
                                             glob_cxt, &inner_cxt, case_arg_cxt))
                        return false;
                }
 
                /* Recurse to ELSE expression. */
                if (!foreign_expr_walker((Node *) ce->defresult,
                                         glob_cxt, &inner_cxt, case_arg_cxt))
                    return false;
 
                /*
                 * Detect whether node is introducing a collation not derived
                 * from a foreign Var.  (If so, we just mark it unsafe for now
                 * rather than immediately returning false, since the parent
                 * node might not care.)  This is the same as for function
                 * nodes, except that the input collation is derived from only
                 * the THEN and ELSE subexpressions.
                 */
                collation = ce->casecollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_CaseTestExpr:
            {
                CaseTestExpr *c = (CaseTestExpr *) node;
 
                /* Punt if we seem not to be inside a CASE arg WHEN. */
                if (!case_arg_cxt)
                    return false;
 
                /*
                 * Otherwise, any nondefault collation attached to the
                 * CaseTestExpr node must be derived from foreign Var(s) in
                 * the CASE arg.
                 */
                collation = c->collation;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (case_arg_cxt->state == FDW_COLLATE_SAFE &&
                         collation == case_arg_cxt->collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_ArrayExpr:
            {
                ArrayExpr  *a = (ArrayExpr *) node;
 
                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) a->elements,
                                         glob_cxt, &inner_cxt, case_arg_cxt))
                    return false;
 
                /*
                 * ArrayExpr must not introduce a collation not derived from
                 * an input foreign Var (same logic as for a function).
                 */
                collation = a->array_collid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_List:
            {
                List       *l = (List *) node;
                ListCell   *lc;
 
                /*
                 * Recurse to component subexpressions.
                 */
                foreach(lc, l)
                {
                    if (!foreign_expr_walker((Node *) lfirst(lc),
                                             glob_cxt, &inner_cxt, case_arg_cxt))
                        return false;
                }
 
                /*
                 * When processing a list, collation state just bubbles up
                 * from the list elements.
                 */
                collation = inner_cxt.collation;
                state = inner_cxt.state;
 
                /* Don't apply exprType() to the list. */
                check_type = false;
            }
            break;
        case T_Aggref:
            {
                Aggref     *agg = (Aggref *) node;
                ListCell   *lc;
 
                /* Not safe to pushdown when not in grouping context */
                if (!IS_UPPER_REL(glob_cxt->foreignrel))
                    return false;
 
                /* Only non-split aggregates are pushable. */
                if (agg->aggsplit != AGGSPLIT_SIMPLE)
                    return false;
 
                /* As usual, it must be shippable. */
                if (!is_shippable(agg->aggfnoid, ProcedureRelationId, fpinfo))
                    return false;
 
                /*
                 * Recurse to input args. aggdirectargs, aggorder and
                 * aggdistinct are all present in args, so no need to check
                 * their shippability explicitly.
                 */
                foreach(lc, agg->args)
                {
                    Node       *n = (Node *) lfirst(lc);
 
                    /* If TargetEntry, extract the expression from it */
                    if (IsA(n, TargetEntry))
                    {
                        TargetEntry *tle = (TargetEntry *) n;
 
                        n = (Node *) tle->expr;
                    }
 
                    if (!foreign_expr_walker(n,
                                             glob_cxt, &inner_cxt, case_arg_cxt))
                        return false;
                }
 
                /*
                 * For aggorder elements, check whether the sort operator, if
                 * specified, is shippable or not.
                 */
                if (agg->aggorder)
                {
                    foreach(lc, agg->aggorder)
                    {
                        SortGroupClause *srt = (SortGroupClause *) lfirst(lc);
                        Oid         sortcoltype;
                        TypeCacheEntry *typentry;
                        TargetEntry *tle;
 
                        tle = get_sortgroupref_tle(srt->tleSortGroupRef,
                                                   agg->args);
                        sortcoltype = exprType((Node *) tle->expr);
                        typentry = lookup_type_cache(sortcoltype,
                                                     TYPECACHE_LT_OPR | TYPECACHE_GT_OPR);
                        /* Check shippability of non-default sort operator. */
                        if (srt->sortop != typentry->lt_opr &&
                            srt->sortop != typentry->gt_opr &&
                            !is_shippable(srt->sortop, OperatorRelationId,
                                          fpinfo))
                            return false;
                    }
                }
 
                /* Check aggregate filter */
                if (!foreign_expr_walker((Node *) agg->aggfilter,
                                         glob_cxt, &inner_cxt, case_arg_cxt))
                    return false;
 
                /*
                 * If aggregate's input collation is not derived from a
                 * foreign Var, it can't be sent to remote.
                 */
                if (agg->inputcollid == InvalidOid)
                     /* OK, inputs are all noncollatable */ ;
                else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                         agg->inputcollid != inner_cxt.collation)
                    return false;
 
                /*
                 * Detect whether node is introducing a collation not derived
                 * from a foreign Var.  (If so, we just mark it unsafe for now
                 * rather than immediately returning false, since the parent
                 * node might not care.)
                 */
                collation = agg->aggcollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        default:
 
            /*
             * If it's anything else, assume it's unsafe.  This list can be
             * expanded later, but don't forget to add deparse support below.
             */
            return false;
    }
 
    /*
     * If result type of given expression is not shippable, it can't be sent
     * to remote because it might have incompatible semantics on remote side.
     */
    if (check_type && !is_shippable(exprType(node), TypeRelationId, fpinfo))
        return false;
 
    /*
     * Now, merge my collation information into my parent's state.
     */
    if (state > outer_cxt->state)
    {
        /* Override previous parent state */
        outer_cxt->collation = collation;
        outer_cxt->state = state;
    }
    else if (state == outer_cxt->state)
    {
        /* Merge, or detect error if there's a collation conflict */
        switch (state)
        {
            case FDW_COLLATE_NONE:
                /* Nothing + nothing is still nothing */
                break;
            case FDW_COLLATE_SAFE:
                if (collation != outer_cxt->collation)
                {
                    /*
                     * Non-default collation always beats default.
                     */
                    if (outer_cxt->collation == DEFAULT_COLLATION_OID)
                    {
                        /* Override previous parent state */
                        outer_cxt->collation = collation;
                    }
                    else if (collation != DEFAULT_COLLATION_OID)
                    {
                        /*
                         * Conflict; show state as indeterminate.  We don't
                         * want to "return false" right away, since parent
                         * node might not care about collation.
                         */
                        outer_cxt->state = FDW_COLLATE_UNSAFE;
                    }
                }
                break;
            case FDW_COLLATE_UNSAFE:
                /* We're still conflicted ... */
                break;
        }
    }
 
    /* It looks OK */
    return true;
}
 
/*
 * Returns true if given expr is something we'd have to send the value of
 * to the foreign server.
 *
 * This should return true when the expression is a shippable node that
 * deparseExpr would add to context->params_list.  Note that we don't care
 * if the expression *contains* such a node, only whether one appears at top
 * level.  We need this to detect cases where setrefs.c would recognize a
 * false match between an fdw_exprs item (which came from the params_list)
 * and an entry in fdw_scan_tlist (which we're considering putting the given
 * expression into).
 */
bool
is_foreign_param(PlannerInfo *root,
                 RelOptInfo *baserel,
                 Expr *expr)
{
    if (expr == NULL)
        return false;
 
    switch (nodeTag(expr))
    {
        case T_Var:
            {
                /* It would have to be sent unless it's a foreign Var */
                Var        *var = (Var *) expr;
                PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) (baserel->fdw_private);
                Relids      relids;
 
                if (IS_UPPER_REL(baserel))
                    relids = fpinfo->outerrel->relids;
                else
                    relids = baserel->relids;
 
                if (bms_is_member(var->varno, relids) && var->varlevelsup == 0)
                    return false;   /* foreign Var, so not a param */
                else
                    return true;    /* it'd have to be a param */
                break;
            }
        case T_Param:
            /* Params always have to be sent to the foreign server */
            return true;
        default:
            break;
    }
    return false;
}
 
/*
 * Returns true if it's safe to push down the sort expression described by
 * 'pathkey' to the foreign server.
 */
bool
is_foreign_pathkey(PlannerInfo *root,
                   RelOptInfo *baserel,
                   PathKey *pathkey)
{
    EquivalenceClass *pathkey_ec = pathkey->pk_eclass;
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) baserel->fdw_private;
 
    /*
     * is_foreign_expr would detect volatile expressions as well, but checking
     * ec_has_volatile here saves some cycles.
     */
    if (pathkey_ec->ec_has_volatile)
        return false;
 
    /* can't push down the sort if the pathkey's opfamily is not shippable */
    if (!is_shippable(pathkey->pk_opfamily, OperatorFamilyRelationId, fpinfo))
        return false;
 
    /* can push if a suitable EC member exists */
    return (find_em_for_rel(root, pathkey_ec, baserel) != NULL);
}
 
/*
 * Convert type OID + typmod info into a type name we can ship to the remote
 * server.  Someplace else had better have verified that this type name is
 * expected to be known on the remote end.
 *
 * This is almost just format_type_with_typemod(), except that if left to its
 * own devices, that function will make schema-qualification decisions based
 * on the local search_path, which is wrong.  We must schema-qualify all
 * type names that are not in pg_catalog.  We assume here that built-in types
 * are all in pg_catalog and need not be qualified; otherwise, qualify.
 */
static char *
deparse_type_name(Oid type_oid, int32 typemod)
{
    bits16      flags = FORMAT_TYPE_TYPEMOD_GIVEN;
 
    if (!is_builtin(type_oid))
        flags |= FORMAT_TYPE_FORCE_QUALIFY;
 
    return format_type_extended(type_oid, typemod, flags);
}
 
/*
 * Build the targetlist for given relation to be deparsed as SELECT clause.
 *
 * The output targetlist contains the columns that need to be fetched from the
 * foreign server for the given relation.  If foreignrel is an upper relation,
 * then the output targetlist can also contain expressions to be evaluated on
 * foreign server.
 */
List *
build_tlist_to_deparse(RelOptInfo *foreignrel)
{
    List       *tlist = NIL;
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
    ListCell   *lc;
 
    /*
     * For an upper relation, we have already built the target list while
     * checking shippability, so just return that.
     */
    if (IS_UPPER_REL(foreignrel))
        return fpinfo->grouped_tlist;
 
    /*
     * We require columns specified in foreignrel->reltarget->exprs and those
     * required for evaluating the local conditions.
     */
    tlist = add_to_flat_tlist(tlist,
                              pull_var_clause((Node *) foreignrel->reltarget->exprs,
                                              PVC_RECURSE_PLACEHOLDERS));
    foreach(lc, fpinfo->local_conds)
    {
        RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);
 
        tlist = add_to_flat_tlist(tlist,
                                  pull_var_clause((Node *) rinfo->clause,
                                                  PVC_RECURSE_PLACEHOLDERS));
    }
 
    return tlist;
}
 
/*
 * Deparse SELECT statement for given relation into buf.
 *
 * tlist contains the list of desired columns to be fetched from foreign server.
 * For a base relation fpinfo->attrs_used is used to construct SELECT clause,
 * hence the tlist is ignored for a base relation.
 *
 * remote_conds is the list of conditions to be deparsed into the WHERE clause
 * (or, in the case of upper relations, into the HAVING clause).
 *
 * If params_list is not NULL, it receives a list of Params and other-relation
 * Vars used in the clauses; these values must be transmitted to the remote
 * server as parameter values.
 *
 * If params_list is NULL, we're generating the query for EXPLAIN purposes,
 * so Params and other-relation Vars should be replaced by dummy values.
 *
 * pathkeys is the list of pathkeys to order the result by.
 *
 * is_subquery is the flag to indicate whether to deparse the specified
 * relation as a subquery.
 *
 * List of columns selected is returned in retrieved_attrs.
 */
void
deparseSelectStmtForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *rel,
                        List *tlist, List *remote_conds, List *pathkeys,
                        bool has_final_sort, bool has_limit, bool is_subquery,
                        List **retrieved_attrs, List **params_list)
{
    deparse_expr_cxt context;
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
    List       *quals;
 
    /*
     * We handle relations for foreign tables, joins between those and upper
     * relations.
     */
    Assert(IS_JOIN_REL(rel) || IS_SIMPLE_REL(rel) || IS_UPPER_REL(rel));
 
    /* Fill portions of context common to upper, join and base relation */
    context.buf = buf;
    context.root = root;
    context.foreignrel = rel;
    context.scanrel = IS_UPPER_REL(rel) ? fpinfo->outerrel : rel;
    context.params_list = params_list;
 
    /* Construct SELECT clause */
    deparseSelectSql(tlist, is_subquery, retrieved_attrs, &context);
 
    /*
     * For upper relations, the WHERE clause is built from the remote
     * conditions of the underlying scan relation; otherwise, we can use the
     * supplied list of remote conditions directly.
     */
    if (IS_UPPER_REL(rel))
    {
        PgFdwRelationInfo *ofpinfo;
 
        ofpinfo = (PgFdwRelationInfo *) fpinfo->outerrel->fdw_private;
        quals = ofpinfo->remote_conds;
    }
    else
        quals = remote_conds;
 
    /* Construct FROM and WHERE clauses */
    deparseFromExpr(quals, &context);
 
    if (IS_UPPER_REL(rel))
    {
        /* Append GROUP BY clause */
        appendGroupByClause(tlist, &context);
 
        /* Append HAVING clause */
        if (remote_conds)
        {
            appendStringInfoString(buf, " HAVING ");
            appendConditions(remote_conds, &context);
        }
    }
 
    /* Add ORDER BY clause if we found any useful pathkeys */
    if (pathkeys)
        appendOrderByClause(pathkeys, has_final_sort, &context);
 
    /* Add LIMIT clause if necessary */
    if (has_limit)
        appendLimitClause(&context);
 
    /* Add any necessary FOR UPDATE/SHARE. */
    deparseLockingClause(&context);
}
 
/*
 * Construct a simple SELECT statement that retrieves desired columns
 * of the specified foreign table, and append it to "buf".  The output
 * contains just "SELECT ... ".
 *
 * We also create an integer List of the columns being retrieved, which is
 * returned to *retrieved_attrs, unless we deparse the specified relation
 * as a subquery.
 *
 * tlist is the list of desired columns.  is_subquery is the flag to
 * indicate whether to deparse the specified relation as a subquery.
 * Read prologue of deparseSelectStmtForRel() for details.
 */
static void
deparseSelectSql(List *tlist, bool is_subquery, List **retrieved_attrs,
                 deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    RelOptInfo *foreignrel = context->foreignrel;
    PlannerInfo *root = context->root;
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
    /*
     * Construct SELECT list
     */
    appendStringInfoString(buf, "SELECT ");
 
    if (is_subquery)
    {
        /*
         * For a relation that is deparsed as a subquery, emit expressions
         * specified in the relation's reltarget.  Note that since this is for
         * the subquery, no need to care about *retrieved_attrs.
         */
        deparseSubqueryTargetList(context);
    }
    else if (IS_JOIN_REL(foreignrel) || IS_UPPER_REL(foreignrel))
    {
        /*
         * For a join or upper relation the input tlist gives the list of
         * columns required to be fetched from the foreign server.
         */
        deparseExplicitTargetList(tlist, false, retrieved_attrs, context);
    }
    else
    {
        /*
         * For a base relation fpinfo->attrs_used gives the list of columns
         * required to be fetched from the foreign server.
         */
        RangeTblEntry *rte = planner_rt_fetch(foreignrel->relid, root);
 
        /*
         * Core code already has some lock on each rel being planned, so we
         * can use NoLock here.
         */
        Relation    rel = table_open(rte->relid, NoLock);
 
        deparseTargetList(buf, rte, foreignrel->relid, rel, false,
                          fpinfo->attrs_used, false, retrieved_attrs);
        table_close(rel, NoLock);
    }
}
 
/*
 * Construct a FROM clause and, if needed, a WHERE clause, and append those to
 * "buf".
 *
 * quals is the list of clauses to be included in the WHERE clause.
 * (These may or may not include RestrictInfo decoration.)
 */
static void
deparseFromExpr(List *quals, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    RelOptInfo *scanrel = context->scanrel;
    List       *additional_conds = NIL;
 
    /* For upper relations, scanrel must be either a joinrel or a baserel */
    Assert(!IS_UPPER_REL(context->foreignrel) ||
           IS_JOIN_REL(scanrel) || IS_SIMPLE_REL(scanrel));
 
    /* Construct FROM clause */
    appendStringInfoString(buf, " FROM ");
    deparseFromExprForRel(buf, context->root, scanrel,
                          (bms_membership(scanrel->relids) == BMS_MULTIPLE),
                          (Index) 0, NULL, &additional_conds,
                          context->params_list);
    appendWhereClause(quals, additional_conds, context);
    if (additional_conds != NIL)
        list_free_deep(additional_conds);
}
 
/*
 * Emit a target list that retrieves the columns specified in attrs_used.
 * This is used for both SELECT and RETURNING targetlists; the is_returning
 * parameter is true only for a RETURNING targetlist.
 *
 * The tlist text is appended to buf, and we also create an integer List
 * of the columns being retrieved, which is returned to *retrieved_attrs.
 *
 * If qualify_col is true, add relation alias before the column name.
 */
static void
deparseTargetList(StringInfo buf,
                  RangeTblEntry *rte,
                  Index rtindex,
                  Relation rel,
                  bool is_returning,
                  Bitmapset *attrs_used,
                  bool qualify_col,
                  List **retrieved_attrs)
{
    TupleDesc   tupdesc = RelationGetDescr(rel);
    bool        have_wholerow;
    bool        first;
    int         i;
 
    *retrieved_attrs = NIL;
 
    /* If there's a whole-row reference, we'll need all the columns. */
    have_wholerow = bms_is_member(0 - FirstLowInvalidHeapAttributeNumber,
                                  attrs_used);
 
    first = true;
    for (i = 1; i <= tupdesc->natts; i++)
    {
        Form_pg_attribute attr = TupleDescAttr(tupdesc, i - 1);
 
        /* Ignore dropped attributes. */
        if (attr->attisdropped)
            continue;
 
        if (have_wholerow ||
            bms_is_member(i - FirstLowInvalidHeapAttributeNumber,
                          attrs_used))
        {
            if (!first)
                appendStringInfoString(buf, ", ");
            else if (is_returning)
                appendStringInfoString(buf, " RETURNING ");
            first = false;
 
            deparseColumnRef(buf, rtindex, i, rte, qualify_col);
 
            *retrieved_attrs = lappend_int(*retrieved_attrs, i);
        }
    }
 
    /*
     * Add ctid if needed.  We currently don't support retrieving any other
     * system columns.
     */
    if (bms_is_member(SelfItemPointerAttributeNumber - FirstLowInvalidHeapAttributeNumber,
                      attrs_used))
    {
        if (!first)
            appendStringInfoString(buf, ", ");
        else if (is_returning)
            appendStringInfoString(buf, " RETURNING ");
        first = false;
 
        if (qualify_col)
            ADD_REL_QUALIFIER(buf, rtindex);
        appendStringInfoString(buf, "ctid");
 
        *retrieved_attrs = lappend_int(*retrieved_attrs,
                                       SelfItemPointerAttributeNumber);
    }
 
    /* Don't generate bad syntax if no undropped columns */
    if (first && !is_returning)
        appendStringInfoString(buf, "NULL");
}
 
/*
 * Deparse the appropriate locking clause (FOR UPDATE or FOR SHARE) for a
 * given relation (context->scanrel).
 */
static void
deparseLockingClause(deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    PlannerInfo *root = context->root;
    RelOptInfo *rel = context->scanrel;
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
    int         relid = -1;
 
    while ((relid = bms_next_member(rel->relids, relid)) >= 0)
    {
        /*
         * Ignore relation if it appears in a lower subquery.  Locking clause
         * for such a relation is included in the subquery if necessary.
         */
        if (bms_is_member(relid, fpinfo->lower_subquery_rels))
            continue;
 
        /*
         * Add FOR UPDATE/SHARE if appropriate.  We apply locking during the
         * initial row fetch, rather than later on as is done for local
         * tables. The extra roundtrips involved in trying to duplicate the
         * local semantics exactly don't seem worthwhile (see also comments
         * for RowMarkType).
         *
         * Note: because we actually run the query as a cursor, this assumes
         * that DECLARE CURSOR ... FOR UPDATE is supported, which it isn't
         * before 8.3.
         */
        if (bms_is_member(relid, root->all_result_relids) &&
            (root->parse->commandType == CMD_UPDATE ||
             root->parse->commandType == CMD_DELETE))
        {
            /* Relation is UPDATE/DELETE target, so use FOR UPDATE */
            appendStringInfoString(buf, " FOR UPDATE");
 
            /* Add the relation alias if we are here for a join relation */
            if (IS_JOIN_REL(rel))
                appendStringInfo(buf, " OF %s%d", REL_ALIAS_PREFIX, relid);
        }
        else
        {
            PlanRowMark *rc = get_plan_rowmark(root->rowMarks, relid);
 
            if (rc)
            {
                /*
                 * Relation is specified as a FOR UPDATE/SHARE target, so
                 * handle that.  (But we could also see LCS_NONE, meaning this
                 * isn't a target relation after all.)
                 *
                 * For now, just ignore any [NO] KEY specification, since (a)
                 * it's not clear what that means for a remote table that we
                 * don't have complete information about, and (b) it wouldn't
                 * work anyway on older remote servers.  Likewise, we don't
                 * worry about NOWAIT.
                 */
                switch (rc->strength)
                {
                    case LCS_NONE:
                        /* No locking needed */
                        break;
                    case LCS_FORKEYSHARE:
                    case LCS_FORSHARE:
                        appendStringInfoString(buf, " FOR SHARE");
                        break;
                    case LCS_FORNOKEYUPDATE:
                    case LCS_FORUPDATE:
                        appendStringInfoString(buf, " FOR UPDATE");
                        break;
                }
 
                /* Add the relation alias if we are here for a join relation */
                if (bms_membership(rel->relids) == BMS_MULTIPLE &&
                    rc->strength != LCS_NONE)
                    appendStringInfo(buf, " OF %s%d", REL_ALIAS_PREFIX, relid);
            }
        }
    }
}
 
/*
 * Deparse conditions from the provided list and append them to buf.
 *
 * The conditions in the list are assumed to be ANDed. This function is used to
 * deparse WHERE clauses, JOIN .. ON clauses and HAVING clauses.
 *
 * Depending on the caller, the list elements might be either RestrictInfos
 * or bare clauses.
 */
static void
appendConditions(List *exprs, deparse_expr_cxt *context)
{
    int         nestlevel;
    ListCell   *lc;
    bool        is_first = true;
    StringInfo  buf = context->buf;
 
    /* Make sure any constants in the exprs are printed portably */
    nestlevel = set_transmission_modes();
 
    foreach(lc, exprs)
    {
        Expr       *expr = (Expr *) lfirst(lc);
 
        /* Extract clause from RestrictInfo, if required */
        if (IsA(expr, RestrictInfo))
            expr = ((RestrictInfo *) expr)->clause;
 
        /* Connect expressions with "AND" and parenthesize each condition. */
        if (!is_first)
            appendStringInfoString(buf, " AND ");
 
        appendStringInfoChar(buf, '(');
        deparseExpr(expr, context);
        appendStringInfoChar(buf, ')');
 
        is_first = false;
    }
 
    reset_transmission_modes(nestlevel);
}
 
/*
 * Append WHERE clause, containing conditions from exprs and additional_conds,
 * to context->buf.
 */
static void
appendWhereClause(List *exprs, List *additional_conds, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    bool        need_and = false;
    ListCell   *lc;
 
    if (exprs != NIL || additional_conds != NIL)
        appendStringInfoString(buf, " WHERE ");
 
    /*
     * If there are some filters, append them.
     */
    if (exprs != NIL)
    {
        appendConditions(exprs, context);
        need_and = true;
    }
 
    /*
     * If there are some EXISTS conditions, coming from SEMI-JOINS, append
     * them.
     */
    foreach(lc, additional_conds)
    {
        if (need_and)
            appendStringInfoString(buf, " AND ");
        appendStringInfoString(buf, (char *) lfirst(lc));
        need_and = true;
    }
}
 
/* Output join name for given join type */
const char *
get_jointype_name(JoinType jointype)
{
    switch (jointype)
    {
        case JOIN_INNER:
            return "INNER";
 
        case JOIN_LEFT:
            return "LEFT";
 
        case JOIN_RIGHT:
            return "RIGHT";
 
        case JOIN_FULL:
            return "FULL";
 
        case JOIN_SEMI:
            return "SEMI";
 
        default:
            /* Shouldn't come here, but protect from buggy code. */
            elog(ERROR, "unsupported join type %d", jointype);
    }
 
    /* Keep compiler happy */
    return NULL;
}
 
/*
 * Deparse given targetlist and append it to context->buf.
 *
 * tlist is list of TargetEntry's which in turn contain Var nodes.
 *
 * retrieved_attrs is the list of continuously increasing integers starting
 * from 1. It has same number of entries as tlist.
 *
 * This is used for both SELECT and RETURNING targetlists; the is_returning
 * parameter is true only for a RETURNING targetlist.
 */
static void
deparseExplicitTargetList(List *tlist,
                          bool is_returning,
                          List **retrieved_attrs,
                          deparse_expr_cxt *context)
{
    ListCell   *lc;
    StringInfo  buf = context->buf;
    int         i = 0;
 
    *retrieved_attrs = NIL;
 
    foreach(lc, tlist)
    {
        TargetEntry *tle = lfirst_node(TargetEntry, lc);
 
        if (i > 0)
            appendStringInfoString(buf, ", ");
        else if (is_returning)
            appendStringInfoString(buf, " RETURNING ");
 
        deparseExpr((Expr *) tle->expr, context);
 
        *retrieved_attrs = lappend_int(*retrieved_attrs, i + 1);
        i++;
    }
 
    if (i == 0 && !is_returning)
        appendStringInfoString(buf, "NULL");
}
 
/*
 * Emit expressions specified in the given relation's reltarget.
 *
 * This is used for deparsing the given relation as a subquery.
 */
static void
deparseSubqueryTargetList(deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    RelOptInfo *foreignrel = context->foreignrel;
    bool        first;
    ListCell   *lc;
 
    /* Should only be called in these cases. */
    Assert(IS_SIMPLE_REL(foreignrel) || IS_JOIN_REL(foreignrel));
 
    first = true;
    foreach(lc, foreignrel->reltarget->exprs)
    {
        Node       *node = (Node *) lfirst(lc);
 
        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;
 
        deparseExpr((Expr *) node, context);
    }
 
    /* Don't generate bad syntax if no expressions */
    if (first)
        appendStringInfoString(buf, "NULL");
}
 
/*
 * Construct FROM clause for given relation
 *
 * The function constructs ... JOIN ... ON ... for join relation. For a base
 * relation it just returns schema-qualified tablename, with the appropriate
 * alias if so requested.
 *
 * 'ignore_rel' is either zero or the RT index of a target relation.  In the
 * latter case the function constructs FROM clause of UPDATE or USING clause
 * of DELETE; it deparses the join relation as if the relation never contained
 * the target relation, and creates a List of conditions to be deparsed into
 * the top-level WHERE clause, which is returned to *ignore_conds.
 *
 * 'additional_conds' is a pointer to a list of strings to be appended to
 * the WHERE clause, coming from lower-level SEMI-JOINs.
 */
static void
deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
                      bool use_alias, Index ignore_rel, List **ignore_conds,
                      List **additional_conds, List **params_list)
{
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
    if (IS_JOIN_REL(foreignrel))
    {
        StringInfoData join_sql_o;
        StringInfoData join_sql_i;
        RelOptInfo *outerrel = fpinfo->outerrel;
        RelOptInfo *innerrel = fpinfo->innerrel;
        bool        outerrel_is_target = false;
        bool        innerrel_is_target = false;
        List       *additional_conds_i = NIL;
        List       *additional_conds_o = NIL;
 
        if (ignore_rel > 0 && bms_is_member(ignore_rel, foreignrel->relids))
        {
            /*
             * If this is an inner join, add joinclauses to *ignore_conds and
             * set it to empty so that those can be deparsed into the WHERE
             * clause.  Note that since the target relation can never be
             * within the nullable side of an outer join, those could safely
             * be pulled up into the WHERE clause (see foreign_join_ok()).
             * Note also that since the target relation is only inner-joined
             * to any other relation in the query, all conditions in the join
             * tree mentioning the target relation could be deparsed into the
             * WHERE clause by doing this recursively.
             */
            if (fpinfo->jointype == JOIN_INNER)
            {
                *ignore_conds = list_concat(*ignore_conds,
                                            fpinfo->joinclauses);
                fpinfo->joinclauses = NIL;
            }
 
            /*
             * Check if either of the input relations is the target relation.
             */
            if (outerrel->relid == ignore_rel)
                outerrel_is_target = true;
            else if (innerrel->relid == ignore_rel)
                innerrel_is_target = true;
        }
 
        /* Deparse outer relation if not the target relation. */
        if (!outerrel_is_target)
        {
            initStringInfo(&join_sql_o);
            deparseRangeTblRef(&join_sql_o, root, outerrel,
                               fpinfo->make_outerrel_subquery,
                               ignore_rel, ignore_conds, &additional_conds_o,
                               params_list);
 
            /*
             * If inner relation is the target relation, skip deparsing it.
             * Note that since the join of the target relation with any other
             * relation in the query is an inner join and can never be within
             * the nullable side of an outer join, the join could be
             * interchanged with higher-level joins (cf. identity 1 on outer
             * join reordering shown in src/backend/optimizer/README), which
             * means it's safe to skip the target-relation deparsing here.
             */
            if (innerrel_is_target)
            {
                Assert(fpinfo->jointype == JOIN_INNER);
                Assert(fpinfo->joinclauses == NIL);
                appendBinaryStringInfo(buf, join_sql_o.data, join_sql_o.len);
                /* Pass EXISTS conditions to upper level */
                if (additional_conds_o != NIL)
                {
                    Assert(*additional_conds == NIL);
                    *additional_conds = additional_conds_o;
                }
                return;
            }
        }
 
        /* Deparse inner relation if not the target relation. */
        if (!innerrel_is_target)
        {
            initStringInfo(&join_sql_i);
            deparseRangeTblRef(&join_sql_i, root, innerrel,
                               fpinfo->make_innerrel_subquery,
                               ignore_rel, ignore_conds, &additional_conds_i,
                               params_list);
 
            /*
             * SEMI-JOIN is deparsed as the EXISTS subquery. It references
             * outer and inner relations, so it should be evaluated as the
             * condition in the upper-level WHERE clause. We deparse the
             * condition and pass it to upper level callers as an
             * additional_conds list. Upper level callers are responsible for
             * inserting conditions from the list where appropriate.
             */
            if (fpinfo->jointype == JOIN_SEMI)
            {
                deparse_expr_cxt context;
                StringInfoData str;
 
                /* Construct deparsed condition from this SEMI-JOIN */
                initStringInfo(&str);
                appendStringInfo(&str, "EXISTS (SELECT NULL FROM %s",
                                 join_sql_i.data);
 
                context.buf = &str;
                context.foreignrel = foreignrel;
                context.scanrel = foreignrel;
                context.root = root;
                context.params_list = params_list;
 
                /*
                 * Append SEMI-JOIN clauses and EXISTS conditions from lower
                 * levels to the current EXISTS subquery
                 */
                appendWhereClause(fpinfo->joinclauses, additional_conds_i, &context);
 
                /*
                 * EXISTS conditions, coming from lower join levels, have just
                 * been processed.
                 */
                if (additional_conds_i != NIL)
                {
                    list_free_deep(additional_conds_i);
                    additional_conds_i = NIL;
                }
 
                /* Close parentheses for EXISTS subquery */
                appendStringInfoChar(&str, ')');
 
                *additional_conds = lappend(*additional_conds, str.data);
            }
 
            /*
             * If outer relation is the target relation, skip deparsing it.
             * See the above note about safety.
             */
            if (outerrel_is_target)
            {
                Assert(fpinfo->jointype == JOIN_INNER);
                Assert(fpinfo->joinclauses == NIL);
                appendBinaryStringInfo(buf, join_sql_i.data, join_sql_i.len);
                /* Pass EXISTS conditions to the upper call */
                if (additional_conds_i != NIL)
                {
                    Assert(*additional_conds == NIL);
                    *additional_conds = additional_conds_i;
                }
                return;
            }
        }
 
        /* Neither of the relations is the target relation. */
        Assert(!outerrel_is_target && !innerrel_is_target);
 
        /*
         * For semijoin FROM clause is deparsed as an outer relation. An inner
         * relation and join clauses are converted to EXISTS condition and
         * passed to the upper level.
         */
        if (fpinfo->jointype == JOIN_SEMI)
        {
            appendBinaryStringInfo(buf, join_sql_o.data, join_sql_o.len);
        }
        else
        {
            /*
             * For a join relation FROM clause, entry is deparsed as
             *
             * ((outer relation) <join type> (inner relation) ON
             * (joinclauses))
             */
            appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
                             get_jointype_name(fpinfo->jointype), join_sql_i.data);
 
            /* Append join clause; (TRUE) if no join clause */
            if (fpinfo->joinclauses)
            {
                deparse_expr_cxt context;
 
                context.buf = buf;
                context.foreignrel = foreignrel;
                context.scanrel = foreignrel;
                context.root = root;
                context.params_list = params_list;
 
                appendStringInfoChar(buf, '(');
                appendConditions(fpinfo->joinclauses, &context);
                appendStringInfoChar(buf, ')');
            }
            else
                appendStringInfoString(buf, "(TRUE)");
 
            /* End the FROM clause entry. */
            appendStringInfoChar(buf, ')');
        }
 
        /*
         * Construct additional_conds to be passed to the upper caller from
         * current level additional_conds and additional_conds, coming from
         * inner and outer rels.
         */
        if (additional_conds_o != NIL)
        {
            *additional_conds = list_concat(*additional_conds,
                                            additional_conds_o);
            list_free(additional_conds_o);
        }
 
        if (additional_conds_i != NIL)
        {
            *additional_conds = list_concat(*additional_conds,
                                            additional_conds_i);
            list_free(additional_conds_i);
        }
    }
    else
    {
        RangeTblEntry *rte = planner_rt_fetch(foreignrel->relid, root);
 
        /*
         * Core code already has some lock on each rel being planned, so we
         * can use NoLock here.
         */
        Relation    rel = table_open(rte->relid, NoLock);
 
        deparseRelation(buf, rel);
 
        /*
         * Add a unique alias to avoid any conflict in relation names due to
         * pulled up subqueries in the query being built for a pushed down
         * join.
         */
        if (use_alias)
            appendStringInfo(buf, " %s%d", REL_ALIAS_PREFIX, foreignrel->relid);
 
        table_close(rel, NoLock);
    }
}
 
/*
 * Append FROM clause entry for the given relation into buf.
 * Conditions from lower-level SEMI-JOINs are appended to additional_conds
 * and should be added to upper level WHERE clause.
 */
static void
deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
                   bool make_subquery, Index ignore_rel, List **ignore_conds,
                   List **additional_conds, List **params_list)
{
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
 
    /* Should only be called in these cases. */
    Assert(IS_SIMPLE_REL(foreignrel) || IS_JOIN_REL(foreignrel));
 
    Assert(fpinfo->local_conds == NIL);
 
    /* If make_subquery is true, deparse the relation as a subquery. */
    if (make_subquery)
    {
        List       *retrieved_attrs;
        int         ncols;
 
        /*
         * The given relation shouldn't contain the target relation, because
         * this should only happen for input relations for a full join, and
         * such relations can never contain an UPDATE/DELETE target.
         */
        Assert(ignore_rel == 0 ||
               !bms_is_member(ignore_rel, foreignrel->relids));
 
        /* Deparse the subquery representing the relation. */
        appendStringInfoChar(buf, '(');
        deparseSelectStmtForRel(buf, root, foreignrel, NIL,
                                fpinfo->remote_conds, NIL,
                                false, false, true,
                                &retrieved_attrs, params_list);
        appendStringInfoChar(buf, ')');
 
        /* Append the relation alias. */
        appendStringInfo(buf, " %s%d", SUBQUERY_REL_ALIAS_PREFIX,
                         fpinfo->relation_index);
 
        /*
         * Append the column aliases if needed.  Note that the subquery emits
         * expressions specified in the relation's reltarget (see
         * deparseSubqueryTargetList).
         */
        ncols = list_length(foreignrel->reltarget->exprs);
        if (ncols > 0)
        {
            int         i;
 
            appendStringInfoChar(buf, '(');
            for (i = 1; i <= ncols; i++)
            {
                if (i > 1)
                    appendStringInfoString(buf, ", ");
 
                appendStringInfo(buf, "%s%d", SUBQUERY_COL_ALIAS_PREFIX, i);
            }
            appendStringInfoChar(buf, ')');
        }
    }
    else
        deparseFromExprForRel(buf, root, foreignrel, true, ignore_rel,
                              ignore_conds, additional_conds,
                              params_list);
}
 
/*
 * deparse remote INSERT statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by WITH CHECK OPTION or RETURNING (if any),
 * which is returned to *retrieved_attrs.
 *
 * This also stores end position of the VALUES clause, so that we can rebuild
 * an INSERT for a batch of rows later.
 */
void
deparseInsertSql(StringInfo buf, RangeTblEntry *rte,
                 Index rtindex, Relation rel,
                 List *targetAttrs, bool doNothing,
                 List *withCheckOptionList, List *returningList,
                 List **retrieved_attrs, int *values_end_len)
{
    TupleDesc   tupdesc = RelationGetDescr(rel);
    AttrNumber  pindex;
    bool        first;
    ListCell   *lc;
 
    appendStringInfoString(buf, "INSERT INTO ");
    deparseRelation(buf, rel);
 
    if (targetAttrs)
    {
        appendStringInfoChar(buf, '(');
 
        first = true;
        foreach(lc, targetAttrs)
        {
            int         attnum = lfirst_int(lc);
 
            if (!first)
                appendStringInfoString(buf, ", ");
            first = false;
 
            deparseColumnRef(buf, rtindex, attnum, rte, false);
        }
 
        appendStringInfoString(buf, ") VALUES (");
 
        pindex = 1;
        first = true;
        foreach(lc, targetAttrs)
        {
            int         attnum = lfirst_int(lc);
            Form_pg_attribute attr = TupleDescAttr(tupdesc, attnum - 1);
 
            if (!first)
                appendStringInfoString(buf, ", ");
            first = false;
 
            if (attr->attgenerated)
                appendStringInfoString(buf, "DEFAULT");
            else
            {
                appendStringInfo(buf, "$%d", pindex);
                pindex++;
            }
        }
 
        appendStringInfoChar(buf, ')');
    }
    else
        appendStringInfoString(buf, " DEFAULT VALUES");
    *values_end_len = buf->len;
 
    if (doNothing)
        appendStringInfoString(buf, " ON CONFLICT DO NOTHING");
 
    deparseReturningList(buf, rte, rtindex, rel,
                         rel->trigdesc && rel->trigdesc->trig_insert_after_row,
                         withCheckOptionList, returningList, retrieved_attrs);
}
 
/*
 * rebuild remote INSERT statement
 *
 * Provided a number of rows in a batch, builds INSERT statement with the
 * right number of parameters.
 */
void
rebuildInsertSql(StringInfo buf, Relation rel,
                 char *orig_query, List *target_attrs,
                 int values_end_len, int num_params,
                 int num_rows)
{
    TupleDesc   tupdesc = RelationGetDescr(rel);
    int         i;
    int         pindex;
    bool        first;
    ListCell   *lc;
 
    /* Make sure the values_end_len is sensible */
    Assert((values_end_len > 0) && (values_end_len <= strlen(orig_query)));
 
    /* Copy up to the end of the first record from the original query */
    appendBinaryStringInfo(buf, orig_query, values_end_len);
 
    /*
     * Add records to VALUES clause (we already have parameters for the first
     * row, so start at the right offset).
     */
    pindex = num_params + 1;
    for (i = 0; i < num_rows; i++)
    {
        appendStringInfoString(buf, ", (");
 
        first = true;
        foreach(lc, target_attrs)
        {
            int         attnum = lfirst_int(lc);
            Form_pg_attribute attr = TupleDescAttr(tupdesc, attnum - 1);
 
            if (!first)
                appendStringInfoString(buf, ", ");
            first = false;
 
            if (attr->attgenerated)
                appendStringInfoString(buf, "DEFAULT");
            else
            {
                appendStringInfo(buf, "$%d", pindex);
                pindex++;
            }
        }
 
        appendStringInfoChar(buf, ')');
    }
 
    /* Copy stuff after VALUES clause from the original query */
    appendStringInfoString(buf, orig_query + values_end_len);
}
 
/*
 * deparse remote UPDATE statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by WITH CHECK OPTION or RETURNING (if any),
 * which is returned to *retrieved_attrs.
 */
void
deparseUpdateSql(StringInfo buf, RangeTblEntry *rte,
                 Index rtindex, Relation rel,
                 List *targetAttrs,
                 List *withCheckOptionList, List *returningList,
                 List **retrieved_attrs)
{
    TupleDesc   tupdesc = RelationGetDescr(rel);
    AttrNumber  pindex;
    bool        first;
    ListCell   *lc;
 
    appendStringInfoString(buf, "UPDATE ");
    deparseRelation(buf, rel);
    appendStringInfoString(buf, " SET ");
 
    pindex = 2;                 /* ctid is always the first param */
    first = true;
    foreach(lc, targetAttrs)
    {
        int         attnum = lfirst_int(lc);
        Form_pg_attribute attr = TupleDescAttr(tupdesc, attnum - 1);
 
        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;
 
        deparseColumnRef(buf, rtindex, attnum, rte, false);
        if (attr->attgenerated)
            appendStringInfoString(buf, " = DEFAULT");
        else
        {
            appendStringInfo(buf, " = $%d", pindex);
            pindex++;
        }
    }
    appendStringInfoString(buf, " WHERE ctid = $1");
 
    deparseReturningList(buf, rte, rtindex, rel,
                         rel->trigdesc && rel->trigdesc->trig_update_after_row,
                         withCheckOptionList, returningList, retrieved_attrs);
}
 
/*
 * deparse remote UPDATE statement
 *
 * 'buf' is the output buffer to append the statement to
 * 'rtindex' is the RT index of the associated target relation
 * 'rel' is the relation descriptor for the target relation
 * 'foreignrel' is the RelOptInfo for the target relation or the join relation
 *      containing all base relations in the query
 * 'targetlist' is the tlist of the underlying foreign-scan plan node
 *      (note that this only contains new-value expressions and junk attrs)
 * 'targetAttrs' is the target columns of the UPDATE
 * 'remote_conds' is the qual clauses that must be evaluated remotely
 * '*params_list' is an output list of exprs that will become remote Params
 * 'returningList' is the RETURNING targetlist
 * '*retrieved_attrs' is an output list of integers of columns being retrieved
 *      by RETURNING (if any)
 */
void
deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
                       Index rtindex, Relation rel,
                       RelOptInfo *foreignrel,
                       List *targetlist,
                       List *targetAttrs,
                       List *remote_conds,
                       List **params_list,
                       List *returningList,
                       List **retrieved_attrs)
{
    deparse_expr_cxt context;
    int         nestlevel;
    bool        first;
    RangeTblEntry *rte = planner_rt_fetch(rtindex, root);
    ListCell   *lc,
               *lc2;
    List       *additional_conds = NIL;
 
    /* Set up context struct for recursion */
    context.root = root;
    context.foreignrel = foreignrel;
    context.scanrel = foreignrel;
    context.buf = buf;
    context.params_list = params_list;
 
    appendStringInfoString(buf, "UPDATE ");
    deparseRelation(buf, rel);
    if (foreignrel->reloptkind == RELOPT_JOINREL)
        appendStringInfo(buf, " %s%d", REL_ALIAS_PREFIX, rtindex);
    appendStringInfoString(buf, " SET ");
 
    /* Make sure any constants in the exprs are printed portably */
    nestlevel = set_transmission_modes();
 
    first = true;
    forboth(lc, targetlist, lc2, targetAttrs)
    {
        TargetEntry *tle = lfirst_node(TargetEntry, lc);
        int         attnum = lfirst_int(lc2);
 
        /* update's new-value expressions shouldn't be resjunk */
        Assert(!tle->resjunk);
 
        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;
 
        deparseColumnRef(buf, rtindex, attnum, rte, false);
        appendStringInfoString(buf, " = ");
        deparseExpr((Expr *) tle->expr, &context);
    }
 
    reset_transmission_modes(nestlevel);
 
    if (foreignrel->reloptkind == RELOPT_JOINREL)
    {
        List       *ignore_conds = NIL;
 
 
        appendStringInfoString(buf, " FROM ");
        deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
                              &ignore_conds, &additional_conds, params_list);
        remote_conds = list_concat(remote_conds, ignore_conds);
    }
 
    appendWhereClause(remote_conds, additional_conds, &context);
 
    if (additional_conds != NIL)
        list_free_deep(additional_conds);
 
    if (foreignrel->reloptkind == RELOPT_JOINREL)
        deparseExplicitTargetList(returningList, true, retrieved_attrs,
                                  &context);
    else
        deparseReturningList(buf, rte, rtindex, rel, false,
                             NIL, returningList, retrieved_attrs);
}
 
/*
 * deparse remote DELETE statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by RETURNING (if any), which is returned
 * to *retrieved_attrs.
 */
void
deparseDeleteSql(StringInfo buf, RangeTblEntry *rte,
                 Index rtindex, Relation rel,
                 List *returningList,
                 List **retrieved_attrs)
{
    appendStringInfoString(buf, "DELETE FROM ");
    deparseRelation(buf, rel);
    appendStringInfoString(buf, " WHERE ctid = $1");
 
    deparseReturningList(buf, rte, rtindex, rel,
                         rel->trigdesc && rel->trigdesc->trig_delete_after_row,
                         NIL, returningList, retrieved_attrs);
}
 
/*
 * deparse remote DELETE statement
 *
 * 'buf' is the output buffer to append the statement to
 * 'rtindex' is the RT index of the associated target relation
 * 'rel' is the relation descriptor for the target relation
 * 'foreignrel' is the RelOptInfo for the target relation or the join relation
 *      containing all base relations in the query
 * 'remote_conds' is the qual clauses that must be evaluated remotely
 * '*params_list' is an output list of exprs that will become remote Params
 * 'returningList' is the RETURNING targetlist
 * '*retrieved_attrs' is an output list of integers of columns being retrieved
 *      by RETURNING (if any)
 */
void
deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
                       Index rtindex, Relation rel,
                       RelOptInfo *foreignrel,
                       List *remote_conds,
                       List **params_list,
                       List *returningList,
                       List **retrieved_attrs)
{
    deparse_expr_cxt context;
    List       *additional_conds = NIL;
 
    /* Set up context struct for recursion */
    context.root = root;
    context.foreignrel = foreignrel;
    context.scanrel = foreignrel;
    context.buf = buf;
    context.params_list = params_list;
 
    appendStringInfoString(buf, "DELETE FROM ");
    deparseRelation(buf, rel);
    if (foreignrel->reloptkind == RELOPT_JOINREL)
        appendStringInfo(buf, " %s%d", REL_ALIAS_PREFIX, rtindex);
 
    if (foreignrel->reloptkind == RELOPT_JOINREL)
    {
        List       *ignore_conds = NIL;
 
        appendStringInfoString(buf, " USING ");
        deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
                              &ignore_conds, &additional_conds, params_list);
        remote_conds = list_concat(remote_conds, ignore_conds);
    }
 
    appendWhereClause(remote_conds, additional_conds, &context);
 
    if (additional_conds != NIL)
        list_free_deep(additional_conds);
 
    if (foreignrel->reloptkind == RELOPT_JOINREL)
        deparseExplicitTargetList(returningList, true, retrieved_attrs,
                                  &context);
    else
        deparseReturningList(buf, planner_rt_fetch(rtindex, root),
                             rtindex, rel, false,
                             NIL, returningList, retrieved_attrs);
}
 
/*
 * Add a RETURNING clause, if needed, to an INSERT/UPDATE/DELETE.
 */
static void
deparseReturningList(StringInfo buf, RangeTblEntry *rte,
                     Index rtindex, Relation rel,
                     bool trig_after_row,
                     List *withCheckOptionList,
                     List *returningList,
                     List **retrieved_attrs)
{
    Bitmapset  *attrs_used = NULL;
 
    if (trig_after_row)
    {
        /* whole-row reference acquires all non-system columns */
        attrs_used =
            bms_make_singleton(0 - FirstLowInvalidHeapAttributeNumber);
    }
 
    if (withCheckOptionList != NIL)
    {
        /*
         * We need the attrs, non-system and system, mentioned in the local
         * query's WITH CHECK OPTION list.
         *
         * Note: we do this to ensure that WCO constraints will be evaluated
         * on the data actually inserted/updated on the remote side, which
         * might differ from the data supplied by the core code, for example
         * as a result of remote triggers.
         */
        pull_varattnos((Node *) withCheckOptionList, rtindex,
                       &attrs_used);
    }
 
    if (returningList != NIL)
    {
        /*
         * We need the attrs, non-system and system, mentioned in the local
         * query's RETURNING list.
         */
        pull_varattnos((Node *) returningList, rtindex,
                       &attrs_used);
    }
 
    if (attrs_used != NULL)
        deparseTargetList(buf, rte, rtindex, rel, true, attrs_used, false,
                          retrieved_attrs);
    else
        *retrieved_attrs = NIL;
}
 
/*
 * Construct SELECT statement to acquire size in blocks of given relation.
 *
 * Note: we use local definition of block size, not remote definition.
 * This is perhaps debatable.
 *
 * Note: pg_relation_size() exists in 8.1 and later.
 */
void
deparseAnalyzeSizeSql(StringInfo buf, Relation rel)
{
    StringInfoData relname;
 
    /* We'll need the remote relation name as a literal. */
    initStringInfo(&relname);
    deparseRelation(&relname, rel);
 
    appendStringInfoString(buf, "SELECT pg_catalog.pg_relation_size(");
    deparseStringLiteral(buf, relname.data);
    appendStringInfo(buf, "::pg_catalog.regclass) / %d", BLCKSZ);
}
 
/*
 * Construct SELECT statement to acquire the number of rows and the relkind of
 * a relation.
 *
 * Note: we just return the remote server's reltuples value, which might
 * be off a good deal, but it doesn't seem worth working harder.  See
 * comments in postgresAcquireSampleRowsFunc.
 */
void
deparseAnalyzeInfoSql(StringInfo buf, Relation rel)
{
    StringInfoData relname;
 
    /* We'll need the remote relation name as a literal. */
    initStringInfo(&relname);
    deparseRelation(&relname, rel);
 
    appendStringInfoString(buf, "SELECT reltuples, relkind FROM pg_catalog.pg_class WHERE oid = ");
    deparseStringLiteral(buf, relname.data);
    appendStringInfoString(buf, "::pg_catalog.regclass");
}
 
/*
 * Construct SELECT statement to acquire sample rows of given relation.
 *
 * SELECT command is appended to buf, and list of columns retrieved
 * is returned to *retrieved_attrs.
 *
 * We only support sampling methods we can decide based on server version.
 * Allowing custom TSM modules (like tsm_system_rows) might be useful, but it
 * would require detecting which extensions are installed, to allow automatic
 * fall-back. Moreover, the methods may use different parameters like number
 * of rows (and not sampling rate). So we leave this for future improvements.
 *
 * Using random() to sample rows on the remote server has the advantage that
 * this works on all PostgreSQL versions (unlike TABLESAMPLE), and that it
 * does the sampling on the remote side (without transferring everything and
 * then discarding most rows).
 *
 * The disadvantage is that we still have to read all rows and evaluate the
 * random(), while TABLESAMPLE (at least with the "system" method) may skip.
 * It's not that different from the "bernoulli" method, though.
 *
 * We could also do "ORDER BY random() LIMIT x", which would always pick
 * the expected number of rows, but it requires sorting so it may be much
 * more expensive (particularly on large tables, which is what the
 * remote sampling is meant to improve).
 */
void
deparseAnalyzeSql(StringInfo buf, Relation rel,
                  PgFdwSamplingMethod sample_method, double sample_frac,
                  List **retrieved_attrs)
{
    Oid         relid = RelationGetRelid(rel);
    TupleDesc   tupdesc = RelationGetDescr(rel);
    int         i;
    char       *colname;
    List       *options;
    ListCell   *lc;
    bool        first = true;
 
    *retrieved_attrs = NIL;
 
    appendStringInfoString(buf, "SELECT ");
    for (i = 0; i < tupdesc->natts; i++)
    {
        /* Ignore dropped columns. */
        if (TupleDescAttr(tupdesc, i)->attisdropped)
            continue;
 
        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;
 
        /* Use attribute name or column_name option. */
        colname = NameStr(TupleDescAttr(tupdesc, i)->attname);
        options = GetForeignColumnOptions(relid, i + 1);
 
        foreach(lc, options)
        {
            DefElem    *def = (DefElem *) lfirst(lc);
 
            if (strcmp(def->defname, "column_name") == 0)
            {
                colname = defGetString(def);
                break;
            }
        }
 
        appendStringInfoString(buf, quote_identifier(colname));
 
        *retrieved_attrs = lappend_int(*retrieved_attrs, i + 1);
    }
 
    /* Don't generate bad syntax for zero-column relation. */
    if (first)
        appendStringInfoString(buf, "NULL");
 
    /*
     * Construct FROM clause, and perhaps WHERE clause too, depending on the
     * selected sampling method.
     */
    appendStringInfoString(buf, " FROM ");
    deparseRelation(buf, rel);
 
    switch (sample_method)
    {
        case ANALYZE_SAMPLE_OFF:
            /* nothing to do here */
            break;
 
        case ANALYZE_SAMPLE_RANDOM:
            appendStringInfo(buf, " WHERE pg_catalog.random() < %f", sample_frac);
            break;
 
        case ANALYZE_SAMPLE_SYSTEM:
            appendStringInfo(buf, " TABLESAMPLE SYSTEM(%f)", (100.0 * sample_frac));
            break;
 
        case ANALYZE_SAMPLE_BERNOULLI:
            appendStringInfo(buf, " TABLESAMPLE BERNOULLI(%f)", (100.0 * sample_frac));
            break;
 
        case ANALYZE_SAMPLE_AUTO:
            /* should have been resolved into actual method */
            elog(ERROR, "unexpected sampling method");
            break;
    }
}
 
/*
 * Construct a simple "TRUNCATE rel" statement
 */
void
deparseTruncateSql(StringInfo buf,
                   List *rels,
                   DropBehavior behavior,
                   bool restart_seqs)
{
    ListCell   *cell;
 
    appendStringInfoString(buf, "TRUNCATE ");
 
    foreach(cell, rels)
    {
        Relation    rel = lfirst(cell);
 
        if (cell != list_head(rels))
            appendStringInfoString(buf, ", ");
 
        deparseRelation(buf, rel);
    }
 
    appendStringInfo(buf, " %s IDENTITY",
                     restart_seqs ? "RESTART" : "CONTINUE");
 
    if (behavior == DROP_RESTRICT)
        appendStringInfoString(buf, " RESTRICT");
    else if (behavior == DROP_CASCADE)
        appendStringInfoString(buf, " CASCADE");
}
 
/*
 * Construct name to use for given column, and emit it into buf.
 * If it has a column_name FDW option, use that instead of attribute name.
 *
 * If qualify_col is true, qualify column name with the alias of relation.
 */
static void
deparseColumnRef(StringInfo buf, int varno, int varattno, RangeTblEntry *rte,
                 bool qualify_col)
{
    /* We support fetching the remote side's CTID and OID. */
    if (varattno == SelfItemPointerAttributeNumber)
    {
        if (qualify_col)
            ADD_REL_QUALIFIER(buf, varno);
        appendStringInfoString(buf, "ctid");
    }
    else if (varattno < 0)
    {
        /*
         * All other system attributes are fetched as 0, except for table OID,
         * which is fetched as the local table OID.  However, we must be
         * careful; the table could be beneath an outer join, in which case it
         * must go to NULL whenever the rest of the row does.
         */
        Oid         fetchval = 0;
 
        if (varattno == TableOidAttributeNumber)
            fetchval = rte->relid;
 
        if (qualify_col)
        {
            appendStringInfoString(buf, "CASE WHEN (");
            ADD_REL_QUALIFIER(buf, varno);
            appendStringInfo(buf, "*)::text IS NOT NULL THEN %u END", fetchval);
        }
        else
            appendStringInfo(buf, "%u", fetchval);
    }
    else if (varattno == 0)
    {
        /* Whole row reference */
        Relation    rel;
        Bitmapset  *attrs_used;
 
        /* Required only to be passed down to deparseTargetList(). */
        List       *retrieved_attrs;
 
        /*
         * The lock on the relation will be held by upper callers, so it's
         * fine to open it with no lock here.
         */
        rel = table_open(rte->relid, NoLock);
 
        /*
         * The local name of the foreign table can not be recognized by the
         * foreign server and the table it references on foreign server might
         * have different column ordering or different columns than those
         * declared locally. Hence we have to deparse whole-row reference as
         * ROW(columns referenced locally). Construct this by deparsing a
         * "whole row" attribute.
         */
        attrs_used = bms_add_member(NULL,
                                    0 - FirstLowInvalidHeapAttributeNumber);
 
        /*
         * In case the whole-row reference is under an outer join then it has
         * to go NULL whenever the rest of the row goes NULL. Deparsing a join
         * query would always involve multiple relations, thus qualify_col
         * would be true.
         */
        if (qualify_col)
        {
            appendStringInfoString(buf, "CASE WHEN (");
            ADD_REL_QUALIFIER(buf, varno);
            appendStringInfoString(buf, "*)::text IS NOT NULL THEN ");
        }
 
        appendStringInfoString(buf, "ROW(");
        deparseTargetList(buf, rte, varno, rel, false, attrs_used, qualify_col,
                          &retrieved_attrs);
        appendStringInfoChar(buf, ')');
 
        /* Complete the CASE WHEN statement started above. */
        if (qualify_col)
            appendStringInfoString(buf, " END");
 
        table_close(rel, NoLock);
        bms_free(attrs_used);
    }
    else
    {
        char       *colname = NULL;
        List       *options;
        ListCell   *lc;
 
        /* varno must not be any of OUTER_VAR, INNER_VAR and INDEX_VAR. */
        Assert(!IS_SPECIAL_VARNO(varno));
 
        /*
         * If it's a column of a foreign table, and it has the column_name FDW
         * option, use that value.
         */
        options = GetForeignColumnOptions(rte->relid, varattno);
        foreach(lc, options)
        {
            DefElem    *def = (DefElem *) lfirst(lc);
 
            if (strcmp(def->defname, "column_name") == 0)
            {
                colname = defGetString(def);
                break;
            }
        }
 
        /*
         * If it's a column of a regular table or it doesn't have column_name
         * FDW option, use attribute name.
         */
        if (colname == NULL)
            colname = get_attname(rte->relid, varattno, false);
 
        if (qualify_col)
            ADD_REL_QUALIFIER(buf, varno);
 
        appendStringInfoString(buf, quote_identifier(colname));
    }
}
 
/*
 * Append remote name of specified foreign table to buf.
 * Use value of table_name FDW option (if any) instead of relation's name.
 * Similarly, schema_name FDW option overrides schema name.
 */
static void
deparseRelation(StringInfo buf, Relation rel)
{
    ForeignTable *table;
    const char *nspname = NULL;
    const char *relname = NULL;
    ListCell   *lc;
 
    /* obtain additional catalog information. */
    table = GetForeignTable(RelationGetRelid(rel));
 
    /*
     * Use value of FDW options if any, instead of the name of object itself.
     */
    foreach(lc, table->options)
    {
        DefElem    *def = (DefElem *) lfirst(lc);
 
        if (strcmp(def->defname, "schema_name") == 0)
            nspname = defGetString(def);
        else if (strcmp(def->defname, "table_name") == 0)
            relname = defGetString(def);
    }
 
    /*
     * Note: we could skip printing the schema name if it's pg_catalog, but
     * that doesn't seem worth the trouble.
     */
    if (nspname == NULL)
        nspname = get_namespace_name(RelationGetNamespace(rel));
    if (relname == NULL)
        relname = RelationGetRelationName(rel);
 
    appendStringInfo(buf, "%s.%s",
                     quote_identifier(nspname), quote_identifier(relname));
}
 
/*
 * Append a SQL string literal representing "val" to buf.
 */
void
deparseStringLiteral(StringInfo buf, const char *val)
{
    const char *valptr;
 
    /*
     * Rather than making assumptions about the remote server's value of
     * standard_conforming_strings, always use E'foo' syntax if there are any
     * backslashes.  This will fail on remote servers before 8.1, but those
     * are long out of support.
     */
    if (strchr(val, '\\') != NULL)
        appendStringInfoChar(buf, ESCAPE_STRING_SYNTAX);
    appendStringInfoChar(buf, '\'');
    for (valptr = val; *valptr; valptr++)
    {
        char        ch = *valptr;
 
        if (SQL_STR_DOUBLE(ch, true))
            appendStringInfoChar(buf, ch);
        appendStringInfoChar(buf, ch);
    }
    appendStringInfoChar(buf, '\'');
}
 
/*
 * Deparse given expression into context->buf.
 *
 * This function must support all the same node types that foreign_expr_walker
 * accepts.
 *
 * Note: unlike ruleutils.c, we just use a simple hard-wired parenthesization
 * scheme: anything more complex than a Var, Const, function call or cast
 * should be self-parenthesized.
 */
static void
deparseExpr(Expr *node, deparse_expr_cxt *context)
{
    if (node == NULL)
        return;
 
    switch (nodeTag(node))
    {
        case T_Var:
            deparseVar((Var *) node, context);
            break;
        case T_Const:
            deparseConst((Const *) node, context, 0);
            break;
        case T_Param:
            deparseParam((Param *) node, context);
            break;
        case T_SubscriptingRef:
            deparseSubscriptingRef((SubscriptingRef *) node, context);
            break;
        case T_FuncExpr:
            deparseFuncExpr((FuncExpr *) node, context);
            break;
        case T_OpExpr:
            deparseOpExpr((OpExpr *) node, context);
            break;
        case T_DistinctExpr:
            deparseDistinctExpr((DistinctExpr *) node, context);
            break;
        case T_ScalarArrayOpExpr:
            deparseScalarArrayOpExpr((ScalarArrayOpExpr *) node, context);
            break;
        case T_RelabelType:
            deparseRelabelType((RelabelType *) node, context);
            break;
        case T_BoolExpr:
            deparseBoolExpr((BoolExpr *) node, context);
            break;
        case T_NullTest:
            deparseNullTest((NullTest *) node, context);
            break;
        case T_CaseExpr:
            deparseCaseExpr((CaseExpr *) node, context);
            break;
        case T_ArrayExpr:
            deparseArrayExpr((ArrayExpr *) node, context);
            break;
        case T_Aggref:
            deparseAggref((Aggref *) node, context);
            break;
        default:
            elog(ERROR, "unsupported expression type for deparse: %d",
                 (int) nodeTag(node));
            break;
    }
}
 
/*
 * Deparse given Var node into context->buf.
 *
 * If the Var belongs to the foreign relation, just print its remote name.
 * Otherwise, it's effectively a Param (and will in fact be a Param at
 * run time).  Handle it the same way we handle plain Params --- see
 * deparseParam for comments.
 */
static void
deparseVar(Var *node, deparse_expr_cxt *context)
{
    Relids      relids = context->scanrel->relids;
    int         relno;
    int         colno;
 
    /* Qualify columns when multiple relations are involved. */
    bool        qualify_col = (bms_membership(relids) == BMS_MULTIPLE);
 
    /*
     * If the Var belongs to the foreign relation that is deparsed as a
     * subquery, use the relation and column alias to the Var provided by the
     * subquery, instead of the remote name.
     */
    if (is_subquery_var(node, context->scanrel, &relno, &colno))
    {
        appendStringInfo(context->buf, "%s%d.%s%d",
                         SUBQUERY_REL_ALIAS_PREFIX, relno,
                         SUBQUERY_COL_ALIAS_PREFIX, colno);
        return;
    }
 
    if (bms_is_member(node->varno, relids) && node->varlevelsup == 0)
        deparseColumnRef(context->buf, node->varno, node->varattno,
                         planner_rt_fetch(node->varno, context->root),
                         qualify_col);
    else
    {
        /* Treat like a Param */
        if (context->params_list)
        {
            int         pindex = 0;
            ListCell   *lc;
 
            /* find its index in params_list */
            foreach(lc, *context->params_list)
            {
                pindex++;
                if (equal(node, (Node *) lfirst(lc)))
                    break;
            }
            if (lc == NULL)
            {
                /* not in list, so add it */
                pindex++;
                *context->params_list = lappend(*context->params_list, node);
            }
 
            printRemoteParam(pindex, node->vartype, node->vartypmod, context);
        }
        else
        {
            printRemotePlaceholder(node->vartype, node->vartypmod, context);
        }
    }
}
 
/*
 * Deparse given constant value into context->buf.
 *
 * This function has to be kept in sync with ruleutils.c's get_const_expr.
 *
 * As in that function, showtype can be -1 to never show "::typename"
 * decoration, +1 to always show it, or 0 to show it only if the constant
 * wouldn't be assumed to be the right type by default.
 *
 * In addition, this code allows showtype to be -2 to indicate that we should
 * not show "::typename" decoration if the constant is printed as an untyped
 * literal or NULL (while in other cases, behaving as for showtype == 0).
 */
static void
deparseConst(Const *node, deparse_expr_cxt *context, int showtype)
{
    StringInfo  buf = context->buf;
    Oid         typoutput;
    bool        typIsVarlena;
    char       *extval;
    bool        isfloat = false;
    bool        isstring = false;
    bool        needlabel;
 
    if (node->constisnull)
    {
        appendStringInfoString(buf, "NULL");
        if (showtype >= 0)
            appendStringInfo(buf, "::%s",
                             deparse_type_name(node->consttype,
                                               node->consttypmod));
        return;
    }
 
    getTypeOutputInfo(node->consttype,
                      &typoutput, &typIsVarlena);
    extval = OidOutputFunctionCall(typoutput, node->constvalue);
 
    switch (node->consttype)
    {
        case INT2OID:
        case INT4OID:
        case INT8OID:
        case OIDOID:
        case FLOAT4OID:
        case FLOAT8OID:
        case NUMERICOID:
            {
                /*
                 * No need to quote unless it's a special value such as 'NaN'.
                 * See comments in get_const_expr().
                 */
                if (strspn(extval, "0123456789+-eE.") == strlen(extval))
                {
                    if (extval[0] == '+' || extval[0] == '-')
                        appendStringInfo(buf, "(%s)", extval);
                    else
                        appendStringInfoString(buf, extval);
                    if (strcspn(extval, "eE.") != strlen(extval))
                        isfloat = true; /* it looks like a float */
                }
                else
                    appendStringInfo(buf, "'%s'", extval);
            }
            break;
        case BITOID:
        case VARBITOID:
            appendStringInfo(buf, "B'%s'", extval);
            break;
        case BOOLOID:
            if (strcmp(extval, "t") == 0)
                appendStringInfoString(buf, "true");
            else
                appendStringInfoString(buf, "false");
            break;
        default:
            deparseStringLiteral(buf, extval);
            isstring = true;
            break;
    }
 
    pfree(extval);
 
    if (showtype == -1)
        return;                 /* never print type label */
 
    /*
     * For showtype == 0, append ::typename unless the constant will be
     * implicitly typed as the right type when it is read in.
     *
     * XXX this code has to be kept in sync with the behavior of the parser,
     * especially make_const.
     */
    switch (node->consttype)
    {
        case BOOLOID:
        case INT4OID:
        case UNKNOWNOID:
            needlabel = false;
            break;
        case NUMERICOID:
            needlabel = !isfloat || (node->consttypmod >= 0);
            break;
        default:
            if (showtype == -2)
            {
                /* label unless we printed it as an untyped string */
                needlabel = !isstring;
            }
            else
                needlabel = true;
            break;
    }
    if (needlabel || showtype > 0)
        appendStringInfo(buf, "::%s",
                         deparse_type_name(node->consttype,
                                           node->consttypmod));
}
 
/*
 * Deparse given Param node.
 *
 * If we're generating the query "for real", add the Param to
 * context->params_list if it's not already present, and then use its index
 * in that list as the remote parameter number.  During EXPLAIN, there's
 * no need to identify a parameter number.
 */
static void
deparseParam(Param *node, deparse_expr_cxt *context)
{
    if (context->params_list)
    {
        int         pindex = 0;
        ListCell   *lc;
 
        /* find its index in params_list */
        foreach(lc, *context->params_list)
        {
            pindex++;
            if (equal(node, (Node *) lfirst(lc)))
                break;
        }
        if (lc == NULL)
        {
            /* not in list, so add it */
            pindex++;
            *context->params_list = lappend(*context->params_list, node);
        }
 
        printRemoteParam(pindex, node->paramtype, node->paramtypmod, context);
    }
    else
    {
        printRemotePlaceholder(node->paramtype, node->paramtypmod, context);
    }
}
 
/*
 * Deparse a container subscript expression.
 */
static void
deparseSubscriptingRef(SubscriptingRef *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    ListCell   *lowlist_item;
    ListCell   *uplist_item;
 
    /* Always parenthesize the expression. */
    appendStringInfoChar(buf, '(');
 
    /*
     * Deparse referenced array expression first.  If that expression includes
     * a cast, we have to parenthesize to prevent the array subscript from
     * being taken as typename decoration.  We can avoid that in the typical
     * case of subscripting a Var, but otherwise do it.
     */
    if (IsA(node->refexpr, Var))
        deparseExpr(node->refexpr, context);
    else
    {
        appendStringInfoChar(buf, '(');
        deparseExpr(node->refexpr, context);
        appendStringInfoChar(buf, ')');
    }
 
    /* Deparse subscript expressions. */
    lowlist_item = list_head(node->reflowerindexpr);    /* could be NULL */
    foreach(uplist_item, node->refupperindexpr)
    {
        appendStringInfoChar(buf, '[');
        if (lowlist_item)
        {
            deparseExpr(lfirst(lowlist_item), context);
            appendStringInfoChar(buf, ':');
            lowlist_item = lnext(node->reflowerindexpr, lowlist_item);
        }
        deparseExpr(lfirst(uplist_item), context);
        appendStringInfoChar(buf, ']');
    }
 
    appendStringInfoChar(buf, ')');
}
 
/*
 * Deparse a function call.
 */
static void
deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    bool        use_variadic;
    bool        first;
    ListCell   *arg;
 
    /*
     * If the function call came from an implicit coercion, then just show the
     * first argument.
     */
    if (node->funcformat == COERCE_IMPLICIT_CAST)
    {
        deparseExpr((Expr *) linitial(node->args), context);
        return;
    }
 
    /*
     * If the function call came from a cast, then show the first argument
     * plus an explicit cast operation.
     */
    if (node->funcformat == COERCE_EXPLICIT_CAST)
    {
        Oid         rettype = node->funcresulttype;
        int32       coercedTypmod;
 
        /* Get the typmod if this is a length-coercion function */
        (void) exprIsLengthCoercion((Node *) node, &coercedTypmod);
 
        deparseExpr((Expr *) linitial(node->args), context);
        appendStringInfo(buf, "::%s",
                         deparse_type_name(rettype, coercedTypmod));
        return;
    }
 
    /* Check if need to print VARIADIC (cf. ruleutils.c) */
    use_variadic = node->funcvariadic;
 
    /*
     * Normal function: display as proname(args).
     */
    appendFunctionName(node->funcid, context);
    appendStringInfoChar(buf, '(');
 
    /* ... and all the arguments */
    first = true;
    foreach(arg, node->args)
    {
        if (!first)
            appendStringInfoString(buf, ", ");
        if (use_variadic && lnext(node->args, arg) == NULL)
            appendStringInfoString(buf, "VARIADIC ");
        deparseExpr((Expr *) lfirst(arg), context);
        first = false;
    }
    appendStringInfoChar(buf, ')');
}
 
/*
 * Deparse given operator expression.   To avoid problems around
 * priority of operations, we always parenthesize the arguments.
 */
static void
deparseOpExpr(OpExpr *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    HeapTuple   tuple;
    Form_pg_operator form;
    Expr       *right;
    bool        canSuppressRightConstCast = false;
    char        oprkind;
 
    /* Retrieve information about the operator from system catalog. */
    tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for operator %u", node->opno);
    form = (Form_pg_operator) GETSTRUCT(tuple);
    oprkind = form->oprkind;
 
    /* Sanity check. */
    Assert((oprkind == 'l' && list_length(node->args) == 1) ||
           (oprkind == 'b' && list_length(node->args) == 2));
 
    right = llast(node->args);
 
    /* Always parenthesize the expression. */
    appendStringInfoChar(buf, '(');
 
    /* Deparse left operand, if any. */
    if (oprkind == 'b')
    {
        Expr       *left = linitial(node->args);
        Oid         leftType = exprType((Node *) left);
        Oid         rightType = exprType((Node *) right);
        bool        canSuppressLeftConstCast = false;
 
        /*
         * When considering a binary operator, if one operand is a Const that
         * can be printed as a bare string literal or NULL (i.e., it will look
         * like type UNKNOWN to the remote parser), the Const normally
         * receives an explicit cast to the operator's input type.  However,
         * in Const-to-Var comparisons where both operands are of the same
         * type, we prefer to suppress the explicit cast, leaving the Const's
         * type resolution up to the remote parser.  The remote's resolution
         * heuristic will assume that an unknown input type being compared to
         * a known input type is of that known type as well.
         *
         * This hack allows some cases to succeed where a remote column is
         * declared with a different type in the local (foreign) table.  By
         * emitting "foreigncol = 'foo'" not "foreigncol = 'foo'::text" or the
         * like, we allow the remote parser to pick an "=" operator that's
         * compatible with whatever type the remote column really is, such as
         * an enum.
         *
         * We allow cast suppression to happen only when the other operand is
         * a plain foreign Var.  Although the remote's unknown-type heuristic
         * would apply to other cases just as well, we would be taking a
         * bigger risk that the inferred type is something unexpected.  With
         * this restriction, if anything goes wrong it's the user's fault for
         * not declaring the local column with the same type as the remote
         * column.
         */
        if (leftType == rightType)
        {
            if (IsA(left, Const))
                canSuppressLeftConstCast = isPlainForeignVar(right, context);
            else if (IsA(right, Const))
                canSuppressRightConstCast = isPlainForeignVar(left, context);
        }
 
        if (canSuppressLeftConstCast)
            deparseConst((Const *) left, context, -2);
        else
            deparseExpr(left, context);
 
        appendStringInfoChar(buf, ' ');
    }
 
    /* Deparse operator name. */
    deparseOperatorName(buf, form);
 
    /* Deparse right operand. */
    appendStringInfoChar(buf, ' ');
 
    if (canSuppressRightConstCast)
        deparseConst((Const *) right, context, -2);
    else
        deparseExpr(right, context);
 
    appendStringInfoChar(buf, ')');
 
    ReleaseSysCache(tuple);
}
 
/*
 * Will "node" deparse as a plain foreign Var?
 */
static bool
isPlainForeignVar(Expr *node, deparse_expr_cxt *context)
{
    /*
     * We allow the foreign Var to have an implicit RelabelType, mainly so
     * that this'll work with varchar columns.  Note that deparseRelabelType
     * will not print such a cast, so we're not breaking the restriction that
     * the expression print as a plain Var.  We won't risk it for an implicit
     * cast that requires a function, nor for non-implicit RelabelType; such
     * cases seem too likely to involve semantics changes compared to what
     * would happen on the remote side.
     */
    if (IsA(node, RelabelType) &&
        ((RelabelType *) node)->relabelformat == COERCE_IMPLICIT_CAST)
        node = ((RelabelType *) node)->arg;
 
    if (IsA(node, Var))
    {
        /*
         * The Var must be one that'll deparse as a foreign column reference
         * (cf. deparseVar).
         */
        Var        *var = (Var *) node;
        Relids      relids = context->scanrel->relids;
 
        if (bms_is_member(var->varno, relids) && var->varlevelsup == 0)
            return true;
    }
 
    return false;
}
 
/*
 * Print the name of an operator.
 */
static void
deparseOperatorName(StringInfo buf, Form_pg_operator opform)
{
    char       *opname;
 
    /* opname is not a SQL identifier, so we should not quote it. */
    opname = NameStr(opform->oprname);
 
    /* Print schema name only if it's not pg_catalog */
    if (opform->oprnamespace != PG_CATALOG_NAMESPACE)
    {
        const char *opnspname;
 
        opnspname = get_namespace_name(opform->oprnamespace);
        /* Print fully qualified operator name. */
        appendStringInfo(buf, "OPERATOR(%s.%s)",
                         quote_identifier(opnspname), opname);
    }
    else
    {
        /* Just print operator name. */
        appendStringInfoString(buf, opname);
    }
}
 
/*
 * Deparse IS DISTINCT FROM.
 */
static void
deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
 
    Assert(list_length(node->args) == 2);
 
    appendStringInfoChar(buf, '(');
    deparseExpr(linitial(node->args), context);
    appendStringInfoString(buf, " IS DISTINCT FROM ");
    deparseExpr(lsecond(node->args), context);
    appendStringInfoChar(buf, ')');
}
 
/*
 * Deparse given ScalarArrayOpExpr expression.  To avoid problems
 * around priority of operations, we always parenthesize the arguments.
 */
static void
deparseScalarArrayOpExpr(ScalarArrayOpExpr *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    HeapTuple   tuple;
    Form_pg_operator form;
    Expr       *arg1;
    Expr       *arg2;
 
    /* Retrieve information about the operator from system catalog. */
    tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for operator %u", node->opno);
    form = (Form_pg_operator) GETSTRUCT(tuple);
 
    /* Sanity check. */
    Assert(list_length(node->args) == 2);
 
    /* Always parenthesize the expression. */
    appendStringInfoChar(buf, '(');
 
    /* Deparse left operand. */
    arg1 = linitial(node->args);
    deparseExpr(arg1, context);
    appendStringInfoChar(buf, ' ');
 
    /* Deparse operator name plus decoration. */
    deparseOperatorName(buf, form);
    appendStringInfo(buf, " %s (", node->useOr ? "ANY" : "ALL");
 
    /* Deparse right operand. */
    arg2 = lsecond(node->args);
    deparseExpr(arg2, context);
 
    appendStringInfoChar(buf, ')');
 
    /* Always parenthesize the expression. */
    appendStringInfoChar(buf, ')');
 
    ReleaseSysCache(tuple);
}
 
/*
 * Deparse a RelabelType (binary-compatible cast) node.
 */
static void
deparseRelabelType(RelabelType *node, deparse_expr_cxt *context)
{
    deparseExpr(node->arg, context);
    if (node->relabelformat != COERCE_IMPLICIT_CAST)
        appendStringInfo(context->buf, "::%s",
                         deparse_type_name(node->resulttype,
                                           node->resulttypmod));
}
 
/*
 * Deparse a BoolExpr node.
 */
static void
deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    const char *op = NULL;      /* keep compiler quiet */
    bool        first;
    ListCell   *lc;
 
    switch (node->boolop)
    {
        case AND_EXPR:
            op = "AND";
            break;
        case OR_EXPR:
            op = "OR";
            break;
        case NOT_EXPR:
            appendStringInfoString(buf, "(NOT ");
            deparseExpr(linitial(node->args), context);
            appendStringInfoChar(buf, ')');
            return;
    }
 
    appendStringInfoChar(buf, '(');
    first = true;
    foreach(lc, node->args)
    {
        if (!first)
            appendStringInfo(buf, " %s ", op);
        deparseExpr((Expr *) lfirst(lc), context);
        first = false;
    }
    appendStringInfoChar(buf, ')');
}
 
/*
 * Deparse IS [NOT] NULL expression.
 */
static void
deparseNullTest(NullTest *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
 
    appendStringInfoChar(buf, '(');
    deparseExpr(node->arg, context);
 
    /*
     * For scalar inputs, we prefer to print as IS [NOT] NULL, which is
     * shorter and traditional.  If it's a rowtype input but we're applying a
     * scalar test, must print IS [NOT] DISTINCT FROM NULL to be semantically
     * correct.
     */
    if (node->argisrow || !type_is_rowtype(exprType((Node *) node->arg)))
    {
        if (node->nulltesttype == IS_NULL)
            appendStringInfoString(buf, " IS NULL)");
        else
            appendStringInfoString(buf, " IS NOT NULL)");
    }
    else
    {
        if (node->nulltesttype == IS_NULL)
            appendStringInfoString(buf, " IS NOT DISTINCT FROM NULL)");
        else
            appendStringInfoString(buf, " IS DISTINCT FROM NULL)");
    }
}
 
/*
 * Deparse CASE expression
 */
static void
deparseCaseExpr(CaseExpr *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    ListCell   *lc;
 
    appendStringInfoString(buf, "(CASE");
 
    /* If this is a CASE arg WHEN then emit the arg expression */
    if (node->arg != NULL)
    {
        appendStringInfoChar(buf, ' ');
        deparseExpr(node->arg, context);
    }
 
    /* Add each condition/result of the CASE clause */
    foreach(lc, node->args)
    {
        CaseWhen   *whenclause = (CaseWhen *) lfirst(lc);
 
        /* WHEN */
        appendStringInfoString(buf, " WHEN ");
        if (node->arg == NULL)  /* CASE WHEN */
            deparseExpr(whenclause->expr, context);
        else                    /* CASE arg WHEN */
        {
            /* Ignore the CaseTestExpr and equality operator. */
            deparseExpr(lsecond(castNode(OpExpr, whenclause->expr)->args),
                        context);
        }
 
        /* THEN */
        appendStringInfoString(buf, " THEN ");
        deparseExpr(whenclause->result, context);
    }
 
    /* add ELSE if present */
    if (node->defresult != NULL)
    {
        appendStringInfoString(buf, " ELSE ");
        deparseExpr(node->defresult, context);
    }
 
    /* append END */
    appendStringInfoString(buf, " END)");
}
 
/*
 * Deparse ARRAY[...] construct.
 */
static void
deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    bool        first = true;
    ListCell   *lc;
 
    appendStringInfoString(buf, "ARRAY[");
    foreach(lc, node->elements)
    {
        if (!first)
            appendStringInfoString(buf, ", ");
        deparseExpr(lfirst(lc), context);
        first = false;
    }
    appendStringInfoChar(buf, ']');
 
    /* If the array is empty, we need an explicit cast to the array type. */
    if (node->elements == NIL)
        appendStringInfo(buf, "::%s",
                         deparse_type_name(node->array_typeid, -1));
}
 
/*
 * Deparse an Aggref node.
 */
static void
deparseAggref(Aggref *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    bool        use_variadic;
 
    /* Only basic, non-split aggregation accepted. */
    Assert(node->aggsplit == AGGSPLIT_SIMPLE);
 
    /* Check if need to print VARIADIC (cf. ruleutils.c) */
    use_variadic = node->aggvariadic;
 
    /* Find aggregate name from aggfnoid which is a pg_proc entry */
    appendFunctionName(node->aggfnoid, context);
    appendStringInfoChar(buf, '(');
 
    /* Add DISTINCT */
    appendStringInfoString(buf, (node->aggdistinct != NIL) ? "DISTINCT " : "");
 
    if (AGGKIND_IS_ORDERED_SET(node->aggkind))
    {
        /* Add WITHIN GROUP (ORDER BY ..) */
        ListCell   *arg;
        bool        first = true;
 
        Assert(!node->aggvariadic);
        Assert(node->aggorder != NIL);
 
        foreach(arg, node->aggdirectargs)
        {
            if (!first)
                appendStringInfoString(buf, ", ");
            first = false;
 
            deparseExpr((Expr *) lfirst(arg), context);
        }
 
        appendStringInfoString(buf, ") WITHIN GROUP (ORDER BY ");
        appendAggOrderBy(node->aggorder, node->args, context);
    }
    else
    {
        /* aggstar can be set only in zero-argument aggregates */
        if (node->aggstar)
            appendStringInfoChar(buf, '*');
        else
        {
            ListCell   *arg;
            bool        first = true;
 
            /* Add all the arguments */
            foreach(arg, node->args)
            {
                TargetEntry *tle = (TargetEntry *) lfirst(arg);
                Node       *n = (Node *) tle->expr;
 
                if (tle->resjunk)
                    continue;
 
                if (!first)
                    appendStringInfoString(buf, ", ");
                first = false;
 
                /* Add VARIADIC */
                if (use_variadic && lnext(node->args, arg) == NULL)
                    appendStringInfoString(buf, "VARIADIC ");
 
                deparseExpr((Expr *) n, context);
            }
        }
 
        /* Add ORDER BY */
        if (node->aggorder != NIL)
        {
            appendStringInfoString(buf, " ORDER BY ");
            appendAggOrderBy(node->aggorder, node->args, context);
        }
    }
 
    /* Add FILTER (WHERE ..) */
    if (node->aggfilter != NULL)
    {
        appendStringInfoString(buf, ") FILTER (WHERE ");
        deparseExpr((Expr *) node->aggfilter, context);
    }
 
    appendStringInfoChar(buf, ')');
}
 
/*
 * Append ORDER BY within aggregate function.
 */
static void
appendAggOrderBy(List *orderList, List *targetList, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    ListCell   *lc;
    bool        first = true;
 
    foreach(lc, orderList)
    {
        SortGroupClause *srt = (SortGroupClause *) lfirst(lc);
        Node       *sortexpr;
 
        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;
 
        /* Deparse the sort expression proper. */
        sortexpr = deparseSortGroupClause(srt->tleSortGroupRef, targetList,
                                          false, context);
        /* Add decoration as needed. */
        appendOrderBySuffix(srt->sortop, exprType(sortexpr), srt->nulls_first,
                            context);
    }
}
 
/*
 * Append the ASC, DESC, USING <OPERATOR> and NULLS FIRST / NULLS LAST parts
 * of an ORDER BY clause.
 */
static void
appendOrderBySuffix(Oid sortop, Oid sortcoltype, bool nulls_first,
                    deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    TypeCacheEntry *typentry;
 
    /* See whether operator is default < or > for sort expr's datatype. */
    typentry = lookup_type_cache(sortcoltype,
                                 TYPECACHE_LT_OPR | TYPECACHE_GT_OPR);
 
    if (sortop == typentry->lt_opr)
        appendStringInfoString(buf, " ASC");
    else if (sortop == typentry->gt_opr)
        appendStringInfoString(buf, " DESC");
    else
    {
        HeapTuple   opertup;
        Form_pg_operator operform;
 
        appendStringInfoString(buf, " USING ");
 
        /* Append operator name. */
        opertup = SearchSysCache1(OPEROID, ObjectIdGetDatum(sortop));
        if (!HeapTupleIsValid(opertup))
            elog(ERROR, "cache lookup failed for operator %u", sortop);
        operform = (Form_pg_operator) GETSTRUCT(opertup);
        deparseOperatorName(buf, operform);
        ReleaseSysCache(opertup);
    }
 
    if (nulls_first)
        appendStringInfoString(buf, " NULLS FIRST");
    else
        appendStringInfoString(buf, " NULLS LAST");
}
 
/*
 * Print the representation of a parameter to be sent to the remote side.
 *
 * Note: we always label the Param's type explicitly rather than relying on
 * transmitting a numeric type OID in PQsendQueryParams().  This allows us to
 * avoid assuming that types have the same OIDs on the remote side as they
 * do locally --- they need only have the same names.
 */
static void
printRemoteParam(int paramindex, Oid paramtype, int32 paramtypmod,
                 deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    char       *ptypename = deparse_type_name(paramtype, paramtypmod);
 
    appendStringInfo(buf, "$%d::%s", paramindex, ptypename);
}
 
/*
 * Print the representation of a placeholder for a parameter that will be
 * sent to the remote side at execution time.
 *
 * This is used when we're just trying to EXPLAIN the remote query.
 * We don't have the actual value of the runtime parameter yet, and we don't
 * want the remote planner to generate a plan that depends on such a value
 * anyway.  Thus, we can't do something simple like "$1::paramtype".
 * Instead, we emit "((SELECT null::paramtype)::paramtype)".
 * In all extant versions of Postgres, the planner will see that as an unknown
 * constant value, which is what we want.  This might need adjustment if we
 * ever make the planner flatten scalar subqueries.  Note: the reason for the
 * apparently useless outer cast is to ensure that the representation as a
 * whole will be parsed as an a_expr and not a select_with_parens; the latter
 * would do the wrong thing in the context "x = ANY(...)".
 */
static void
printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
                       deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    char       *ptypename = deparse_type_name(paramtype, paramtypmod);
 
    appendStringInfo(buf, "((SELECT null::%s)::%s)", ptypename, ptypename);
}
 
/*
 * Deparse GROUP BY clause.
 */
static void
appendGroupByClause(List *tlist, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    Query      *query = context->root->parse;
    ListCell   *lc;
    bool        first = true;
 
    /* Nothing to be done, if there's no GROUP BY clause in the query. */
    if (!query->groupClause)
        return;
 
    appendStringInfoString(buf, " GROUP BY ");
 
    /*
     * Queries with grouping sets are not pushed down, so we don't expect
     * grouping sets here.
     */
    Assert(!query->groupingSets);
 
    /*
     * We intentionally print query->groupClause not processed_groupClause,
     * leaving it to the remote planner to get rid of any redundant GROUP BY
     * items again.  This is necessary in case processed_groupClause reduced
     * to empty, and in any case the redundancy situation on the remote might
     * be different than what we think here.
     */
    foreach(lc, query->groupClause)
    {
        SortGroupClause *grp = (SortGroupClause *) lfirst(lc);
 
        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;
 
        deparseSortGroupClause(grp->tleSortGroupRef, tlist, true, context);
    }
}
 
/*
 * Deparse ORDER BY clause defined by the given pathkeys.
 *
 * The clause should use Vars from context->scanrel if !has_final_sort,
 * or from context->foreignrel's targetlist if has_final_sort.
 *
 * We find a suitable pathkey expression (some earlier step
 * should have verified that there is one) and deparse it.
 */
static void
appendOrderByClause(List *pathkeys, bool has_final_sort,
                    deparse_expr_cxt *context)
{
    ListCell   *lcell;
    int         nestlevel;
    StringInfo  buf = context->buf;
    bool        gotone = false;
 
    /* Make sure any constants in the exprs are printed portably */
    nestlevel = set_transmission_modes();
 
    foreach(lcell, pathkeys)
    {
        PathKey    *pathkey = lfirst(lcell);
        EquivalenceMember *em;
        Expr       *em_expr;
        Oid         oprid;
 
        if (has_final_sort)
        {
            /*
             * By construction, context->foreignrel is the input relation to
             * the final sort.
             */
            em = find_em_for_rel_target(context->root,
                                        pathkey->pk_eclass,
                                        context->foreignrel);
        }
        else
            em = find_em_for_rel(context->root,
                                 pathkey->pk_eclass,
                                 context->scanrel);
 
        /*
         * We don't expect any error here; it would mean that shippability
         * wasn't verified earlier.  For the same reason, we don't recheck
         * shippability of the sort operator.
         */
        if (em == NULL)
            elog(ERROR, "could not find pathkey item to sort");
 
        em_expr = em->em_expr;
 
        /*
         * If the member is a Const expression then we needn't add it to the
         * ORDER BY clause.  This can happen in UNION ALL queries where the
         * union child targetlist has a Const.  Adding these would be
         * wasteful, but also, for INT columns, an integer literal would be
         * seen as an ordinal column position rather than a value to sort by.
         * deparseConst() does have code to handle this, but it seems less
         * effort on all accounts just to skip these for ORDER BY clauses.
         */
        if (IsA(em_expr, Const))
            continue;
 
        if (!gotone)
        {
            appendStringInfoString(buf, " ORDER BY ");
            gotone = true;
        }
        else
            appendStringInfoString(buf, ", ");
 
        /*
         * Lookup the operator corresponding to the compare type in the
         * opclass. The datatype used by the opfamily is not necessarily the
         * same as the expression type (for array types for example).
         */
        oprid = get_opfamily_member_for_cmptype(pathkey->pk_opfamily,
                                                em->em_datatype,
                                                em->em_datatype,
                                                pathkey->pk_cmptype);
        if (!OidIsValid(oprid))
            elog(ERROR, "missing operator %d(%u,%u) in opfamily %u",
                 pathkey->pk_cmptype, em->em_datatype, em->em_datatype,
                 pathkey->pk_opfamily);
 
        deparseExpr(em_expr, context);
 
        /*
         * Here we need to use the expression's actual type to discover
         * whether the desired operator will be the default or not.
         */
        appendOrderBySuffix(oprid, exprType((Node *) em_expr),
                            pathkey->pk_nulls_first, context);
 
    }
    reset_transmission_modes(nestlevel);
}
 
/*
 * Deparse LIMIT/OFFSET clause.
 */
static void
appendLimitClause(deparse_expr_cxt *context)
{
    PlannerInfo *root = context->root;
    StringInfo  buf = context->buf;
    int         nestlevel;
 
    /* Make sure any constants in the exprs are printed portably */
    nestlevel = set_transmission_modes();
 
    if (root->parse->limitCount)
    {
        appendStringInfoString(buf, " LIMIT ");
        deparseExpr((Expr *) root->parse->limitCount, context);
    }
    if (root->parse->limitOffset)
    {
        appendStringInfoString(buf, " OFFSET ");
        deparseExpr((Expr *) root->parse->limitOffset, context);
    }
 
    reset_transmission_modes(nestlevel);
}
 
/*
 * appendFunctionName
 *      Deparses function name from given function oid.
 */
static void
appendFunctionName(Oid funcid, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    HeapTuple   proctup;
    Form_pg_proc procform;
    const char *proname;
 
    proctup = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcid));
    if (!HeapTupleIsValid(proctup))
        elog(ERROR, "cache lookup failed for function %u", funcid);
    procform = (Form_pg_proc) GETSTRUCT(proctup);
 
    /* Print schema name only if it's not pg_catalog */
    if (procform->pronamespace != PG_CATALOG_NAMESPACE)
    {
        const char *schemaname;
 
        schemaname = get_namespace_name(procform->pronamespace);
        appendStringInfo(buf, "%s.", quote_identifier(schemaname));
    }
 
    /* Always print the function name */
    proname = NameStr(procform->proname);
    appendStringInfoString(buf, quote_identifier(proname));
 
    ReleaseSysCache(proctup);
}
 
/*
 * Appends a sort or group clause.
 *
 * Like get_rule_sortgroupclause(), returns the expression tree, so caller
 * need not find it again.
 */
static Node *
deparseSortGroupClause(Index ref, List *tlist, bool force_colno,
                       deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    TargetEntry *tle;
    Expr       *expr;
 
    tle = get_sortgroupref_tle(ref, tlist);
    expr = tle->expr;
 
    if (force_colno)
    {
        /* Use column-number form when requested by caller. */
        Assert(!tle->resjunk);
        appendStringInfo(buf, "%d", tle->resno);
    }
    else if (expr && IsA(expr, Const))
    {
        /*
         * Force a typecast here so that we don't emit something like "GROUP
         * BY 2", which will be misconstrued as a column position rather than
         * a constant.
         */
        deparseConst((Const *) expr, context, 1);
    }
    else if (!expr || IsA(expr, Var))
        deparseExpr(expr, context);
    else
    {
        /* Always parenthesize the expression. */
        appendStringInfoChar(buf, '(');
        deparseExpr(expr, context);
        appendStringInfoChar(buf, ')');
    }
 
    return (Node *) expr;
}
 
 
/*
 * Returns true if given Var is deparsed as a subquery output column, in
 * which case, *relno and *colno are set to the IDs for the relation and
 * column alias to the Var provided by the subquery.
 */
static bool
is_subquery_var(Var *node, RelOptInfo *foreignrel, int *relno, int *colno)
{
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
    RelOptInfo *outerrel = fpinfo->outerrel;
    RelOptInfo *innerrel = fpinfo->innerrel;
 
    /* Should only be called in these cases. */
    Assert(IS_SIMPLE_REL(foreignrel) || IS_JOIN_REL(foreignrel));
 
    /*
     * If the given relation isn't a join relation, it doesn't have any lower
     * subqueries, so the Var isn't a subquery output column.
     */
    if (!IS_JOIN_REL(foreignrel))
        return false;
 
    /*
     * If the Var doesn't belong to any lower subqueries, it isn't a subquery
     * output column.
     */
    if (!bms_is_member(node->varno, fpinfo->lower_subquery_rels))
        return false;
 
    if (bms_is_member(node->varno, outerrel->relids))
    {
        /*
         * If outer relation is deparsed as a subquery, the Var is an output
         * column of the subquery; get the IDs for the relation/column alias.
         */
        if (fpinfo->make_outerrel_subquery)
        {
            get_relation_column_alias_ids(node, outerrel, relno, colno);
            return true;
        }
 
        /* Otherwise, recurse into the outer relation. */
        return is_subquery_var(node, outerrel, relno, colno);
    }
    else
    {
        Assert(bms_is_member(node->varno, innerrel->relids));
 
        /*
         * If inner relation is deparsed as a subquery, the Var is an output
         * column of the subquery; get the IDs for the relation/column alias.
         */
        if (fpinfo->make_innerrel_subquery)
        {
            get_relation_column_alias_ids(node, innerrel, relno, colno);
            return true;
        }
 
        /* Otherwise, recurse into the inner relation. */
        return is_subquery_var(node, innerrel, relno, colno);
    }
}
 
/*
 * Get the IDs for the relation and column alias to given Var belonging to
 * given relation, which are returned into *relno and *colno.
 */
static void
get_relation_column_alias_ids(Var *node, RelOptInfo *foreignrel,
                              int *relno, int *colno)
{
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
    int         i;
    ListCell   *lc;
 
    /* Get the relation alias ID */
    *relno = fpinfo->relation_index;
 
    /* Get the column alias ID */
    i = 1;
    foreach(lc, foreignrel->reltarget->exprs)
    {
        Var        *tlvar = (Var *) lfirst(lc);
 
        /*
         * Match reltarget entries only on varno/varattno.  Ideally there
         * would be some cross-check on varnullingrels, but it's unclear what
         * to do exactly; we don't have enough context to know what that value
         * should be.
         */
        if (IsA(tlvar, Var) &&
            tlvar->varno == node->varno &&
            tlvar->varattno == node->varattno)
        {
            *colno = i;
            return;
        }
        i++;
    }
 
    /* Shouldn't get here */
    elog(ERROR, "unexpected expression in subquery output");
}