var.c

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/*-------------------------------------------------------------------------
 *
 * var.c
 *    Var node manipulation routines
 *
 * Note: for most purposes, PlaceHolderVar is considered a Var too,
 * even if its contained expression is variable-free.  Also, CurrentOfExpr
 * is treated as a Var for purposes of determining whether an expression
 * contains variables.
 *
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/optimizer/util/var.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/sysattr.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/optimizer.h"
#include "optimizer/placeholder.h"
#include "optimizer/prep.h"
#include "parser/parsetree.h"
#include "rewrite/rewriteManip.h"
 
 
typedef struct
{
    Relids      varnos;
    PlannerInfo *root;
    int         sublevels_up;
} pull_varnos_context;
 
typedef struct
{
    Bitmapset  *varattnos;
    Index       varno;
} pull_varattnos_context;
 
typedef struct
{
    List       *vars;
    int         sublevels_up;
} pull_vars_context;
 
typedef struct
{
    int         var_location;
    int         sublevels_up;
} locate_var_of_level_context;
 
typedef struct
{
    List       *varlist;
    int         flags;
} pull_var_clause_context;
 
typedef struct
{
    PlannerInfo *root;          /* could be NULL! */
    Query      *query;          /* outer Query */
    int         sublevels_up;
    bool        possible_sublink;   /* could aliases include a SubLink? */
    bool        inserted_sublink;   /* have we inserted a SubLink? */
} flatten_join_alias_vars_context;
 
static bool pull_varnos_walker(Node *node,
                               pull_varnos_context *context);
static bool pull_varattnos_walker(Node *node, pull_varattnos_context *context);
static bool pull_vars_walker(Node *node, pull_vars_context *context);
static bool contain_var_clause_walker(Node *node, void *context);
static bool contain_vars_of_level_walker(Node *node, int *sublevels_up);
static bool locate_var_of_level_walker(Node *node,
                                       locate_var_of_level_context *context);
static bool pull_var_clause_walker(Node *node,
                                   pull_var_clause_context *context);
static Node *flatten_join_alias_vars_mutator(Node *node,
                                             flatten_join_alias_vars_context *context);
static Node *flatten_group_exprs_mutator(Node *node,
                                         flatten_join_alias_vars_context *context);
static Node *mark_nullable_by_grouping(PlannerInfo *root, Node *newnode,
                                       Var *oldvar);
static Node *add_nullingrels_if_needed(PlannerInfo *root, Node *newnode,
                                       Var *oldvar);
static bool is_standard_join_alias_expression(Node *newnode, Var *oldvar);
static void adjust_standard_join_alias_expression(Node *newnode, Var *oldvar);
static Relids alias_relid_set(Query *query, Relids relids);
 
 
/*
 * pull_varnos
 *      Create a set of all the distinct varnos present in a parsetree.
 *      Only varnos that reference level-zero rtable entries are considered.
 *
 * The result includes outer-join relids mentioned in Var.varnullingrels and
 * PlaceHolderVar.phnullingrels fields in the parsetree.
 *
 * "root" can be passed as NULL if it is not necessary to process
 * PlaceHolderVars.
 *
 * NOTE: this is used on not-yet-planned expressions.  It may therefore find
 * bare SubLinks, and if so it needs to recurse into them to look for uplevel
 * references to the desired rtable level!  But when we find a completed
 * SubPlan, we only need to look at the parameters passed to the subplan.
 */
Relids
pull_varnos(PlannerInfo *root, Node *node)
{
    pull_varnos_context context;
 
    context.varnos = NULL;
    context.root = root;
    context.sublevels_up = 0;
 
    /*
     * Must be prepared to start with a Query or a bare expression tree; if
     * it's a Query, we don't want to increment sublevels_up.
     */
    query_or_expression_tree_walker(node,
                                    pull_varnos_walker,
                                    (void *) &context,
                                    0);
 
    return context.varnos;
}
 
/*
 * pull_varnos_of_level
 *      Create a set of all the distinct varnos present in a parsetree.
 *      Only Vars of the specified level are considered.
 */
Relids
pull_varnos_of_level(PlannerInfo *root, Node *node, int levelsup)
{
    pull_varnos_context context;
 
    context.varnos = NULL;
    context.root = root;
    context.sublevels_up = levelsup;
 
    /*
     * Must be prepared to start with a Query or a bare expression tree; if
     * it's a Query, we don't want to increment sublevels_up.
     */
    query_or_expression_tree_walker(node,
                                    pull_varnos_walker,
                                    (void *) &context,
                                    0);
 
    return context.varnos;
}
 
static bool
pull_varnos_walker(Node *node, pull_varnos_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
 
        if (var->varlevelsup == context->sublevels_up)
        {
            context->varnos = bms_add_member(context->varnos, var->varno);
            context->varnos = bms_add_members(context->varnos,
                                              var->varnullingrels);
        }
        return false;
    }
    if (IsA(node, CurrentOfExpr))
    {
        CurrentOfExpr *cexpr = (CurrentOfExpr *) node;
 
        if (context->sublevels_up == 0)
            context->varnos = bms_add_member(context->varnos, cexpr->cvarno);
        return false;
    }
    if (IsA(node, PlaceHolderVar))
    {
        PlaceHolderVar *phv = (PlaceHolderVar *) node;
 
        /*
         * If a PlaceHolderVar is not of the target query level, ignore it,
         * instead recursing into its expression to see if it contains any
         * vars that are of the target level.  We'll also do that when the
         * caller doesn't pass a "root" pointer.  (We probably shouldn't see
         * PlaceHolderVars at all in such cases, but if we do, this is a
         * reasonable behavior.)
         */
        if (phv->phlevelsup == context->sublevels_up &&
            context->root != NULL)
        {
            /*
             * Ideally, the PHV's contribution to context->varnos is its
             * ph_eval_at set.  However, this code can be invoked before
             * that's been computed.  If we cannot find a PlaceHolderInfo,
             * fall back to the conservative assumption that the PHV will be
             * evaluated at its syntactic level (phv->phrels).
             *
             * Another problem is that a PlaceHolderVar can appear in quals or
             * tlists that have been translated for use in a child appendrel.
             * Typically such a PHV is a parameter expression sourced by some
             * other relation, so that the translation from parent appendrel
             * to child doesn't change its phrels, and we should still take
             * ph_eval_at at face value.  But in corner cases, the PHV's
             * original phrels can include the parent appendrel itself, in
             * which case the translated PHV will have the child appendrel in
             * phrels, and we must translate ph_eval_at to match.
             */
            PlaceHolderInfo *phinfo = NULL;
 
            if (phv->phlevelsup == 0)
            {
                if (phv->phid < context->root->placeholder_array_size)
                    phinfo = context->root->placeholder_array[phv->phid];
            }
            if (phinfo == NULL)
            {
                /* No PlaceHolderInfo yet, use phrels */
                context->varnos = bms_add_members(context->varnos,
                                                  phv->phrels);
            }
            else if (bms_equal(phv->phrels, phinfo->ph_var->phrels))
            {
                /* Normal case: use ph_eval_at */
                context->varnos = bms_add_members(context->varnos,
                                                  phinfo->ph_eval_at);
            }
            else
            {
                /* Translated PlaceHolderVar: translate ph_eval_at to match */
                Relids      newevalat,
                            delta;
 
                /* remove what was removed from phv->phrels ... */
                delta = bms_difference(phinfo->ph_var->phrels, phv->phrels);
                newevalat = bms_difference(phinfo->ph_eval_at, delta);
                /* ... then if that was in fact part of ph_eval_at ... */
                if (!bms_equal(newevalat, phinfo->ph_eval_at))
                {
                    /* ... add what was added */
                    delta = bms_difference(phv->phrels, phinfo->ph_var->phrels);
                    newevalat = bms_join(newevalat, delta);
                }
                context->varnos = bms_join(context->varnos,
                                           newevalat);
            }
 
            /*
             * In all three cases, include phnullingrels in the result.  We
             * don't worry about possibly needing to translate it, because
             * appendrels only translate varnos of baserels, not outer joins.
             */
            context->varnos = bms_add_members(context->varnos,
                                              phv->phnullingrels);
            return false;       /* don't recurse into expression */
        }
    }
    else if (IsA(node, Query))
    {
        /* Recurse into RTE subquery or not-yet-planned sublink subquery */
        bool        result;
 
        context->sublevels_up++;
        result = query_tree_walker((Query *) node, pull_varnos_walker,
                                   (void *) context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, pull_varnos_walker,
                                  (void *) context);
}
 
 
/*
 * pull_varattnos
 *      Find all the distinct attribute numbers present in an expression tree,
 *      and add them to the initial contents of *varattnos.
 *      Only Vars of the given varno and rtable level zero are considered.
 *
 * Attribute numbers are offset by FirstLowInvalidHeapAttributeNumber so that
 * we can include system attributes (e.g., OID) in the bitmap representation.
 *
 * Currently, this does not support unplanned subqueries; that is not needed
 * for current uses.  It will handle already-planned SubPlan nodes, though,
 * looking into only the "testexpr" and the "args" list.  (The subplan cannot
 * contain any other references to Vars of the current level.)
 */
void
pull_varattnos(Node *node, Index varno, Bitmapset **varattnos)
{
    pull_varattnos_context context;
 
    context.varattnos = *varattnos;
    context.varno = varno;
 
    (void) pull_varattnos_walker(node, &context);
 
    *varattnos = context.varattnos;
}
 
static bool
pull_varattnos_walker(Node *node, pull_varattnos_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
 
        if (var->varno == context->varno && var->varlevelsup == 0)
            context->varattnos =
                bms_add_member(context->varattnos,
                               var->varattno - FirstLowInvalidHeapAttributeNumber);
        return false;
    }
 
    /* Should not find an unplanned subquery */
    Assert(!IsA(node, Query));
 
    return expression_tree_walker(node, pull_varattnos_walker,
                                  (void *) context);
}
 
 
/*
 * pull_vars_of_level
 *      Create a list of all Vars (and PlaceHolderVars) referencing the
 *      specified query level in the given parsetree.
 *
 * Caution: the Vars are not copied, only linked into the list.
 */
List *
pull_vars_of_level(Node *node, int levelsup)
{
    pull_vars_context context;
 
    context.vars = NIL;
    context.sublevels_up = levelsup;
 
    /*
     * Must be prepared to start with a Query or a bare expression tree; if
     * it's a Query, we don't want to increment sublevels_up.
     */
    query_or_expression_tree_walker(node,
                                    pull_vars_walker,
                                    (void *) &context,
                                    0);
 
    return context.vars;
}
 
static bool
pull_vars_walker(Node *node, pull_vars_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
 
        if (var->varlevelsup == context->sublevels_up)
            context->vars = lappend(context->vars, var);
        return false;
    }
    if (IsA(node, PlaceHolderVar))
    {
        PlaceHolderVar *phv = (PlaceHolderVar *) node;
 
        if (phv->phlevelsup == context->sublevels_up)
            context->vars = lappend(context->vars, phv);
        /* we don't want to look into the contained expression */
        return false;
    }
    if (IsA(node, Query))
    {
        /* Recurse into RTE subquery or not-yet-planned sublink subquery */
        bool        result;
 
        context->sublevels_up++;
        result = query_tree_walker((Query *) node, pull_vars_walker,
                                   (void *) context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, pull_vars_walker,
                                  (void *) context);
}
 
 
/*
 * contain_var_clause
 *    Recursively scan a clause to discover whether it contains any Var nodes
 *    (of the current query level).
 *
 *    Returns true if any varnode found.
 *
 * Does not examine subqueries, therefore must only be used after reduction
 * of sublinks to subplans!
 */
bool
contain_var_clause(Node *node)
{
    return contain_var_clause_walker(node, NULL);
}
 
static bool
contain_var_clause_walker(Node *node, void *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Var))
    {
        if (((Var *) node)->varlevelsup == 0)
            return true;        /* abort the tree traversal and return true */
        return false;
    }
    if (IsA(node, CurrentOfExpr))
        return true;
    if (IsA(node, PlaceHolderVar))
    {
        if (((PlaceHolderVar *) node)->phlevelsup == 0)
            return true;        /* abort the tree traversal and return true */
        /* else fall through to check the contained expr */
    }
    return expression_tree_walker(node, contain_var_clause_walker, context);
}
 
 
/*
 * contain_vars_of_level
 *    Recursively scan a clause to discover whether it contains any Var nodes
 *    of the specified query level.
 *
 *    Returns true if any such Var found.
 *
 * Will recurse into sublinks.  Also, may be invoked directly on a Query.
 */
bool
contain_vars_of_level(Node *node, int levelsup)
{
    int         sublevels_up = levelsup;
 
    return query_or_expression_tree_walker(node,
                                           contain_vars_of_level_walker,
                                           (void *) &sublevels_up,
                                           0);
}
 
static bool
contain_vars_of_level_walker(Node *node, int *sublevels_up)
{
    if (node == NULL)
        return false;
    if (IsA(node, Var))
    {
        if (((Var *) node)->varlevelsup == *sublevels_up)
            return true;        /* abort tree traversal and return true */
        return false;
    }
    if (IsA(node, CurrentOfExpr))
    {
        if (*sublevels_up == 0)
            return true;
        return false;
    }
    if (IsA(node, PlaceHolderVar))
    {
        if (((PlaceHolderVar *) node)->phlevelsup == *sublevels_up)
            return true;        /* abort the tree traversal and return true */
        /* else fall through to check the contained expr */
    }
    if (IsA(node, Query))
    {
        /* Recurse into subselects */
        bool        result;
 
        (*sublevels_up)++;
        result = query_tree_walker((Query *) node,
                                   contain_vars_of_level_walker,
                                   (void *) sublevels_up,
                                   0);
        (*sublevels_up)--;
        return result;
    }
    return expression_tree_walker(node,
                                  contain_vars_of_level_walker,
                                  (void *) sublevels_up);
}
 
 
/*
 * locate_var_of_level
 *    Find the parse location of any Var of the specified query level.
 *
 * Returns -1 if no such Var is in the querytree, or if they all have
 * unknown parse location.  (The former case is probably caller error,
 * but we don't bother to distinguish it from the latter case.)
 *
 * Will recurse into sublinks.  Also, may be invoked directly on a Query.
 *
 * Note: it might seem appropriate to merge this functionality into
 * contain_vars_of_level, but that would complicate that function's API.
 * Currently, the only uses of this function are for error reporting,
 * and so shaving cycles probably isn't very important.
 */
int
locate_var_of_level(Node *node, int levelsup)
{
    locate_var_of_level_context context;
 
    context.var_location = -1;  /* in case we find nothing */
    context.sublevels_up = levelsup;
 
    (void) query_or_expression_tree_walker(node,
                                           locate_var_of_level_walker,
                                           (void *) &context,
                                           0);
 
    return context.var_location;
}
 
static bool
locate_var_of_level_walker(Node *node,
                           locate_var_of_level_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
 
        if (var->varlevelsup == context->sublevels_up &&
            var->location >= 0)
        {
            context->var_location = var->location;
            return true;        /* abort tree traversal and return true */
        }
        return false;
    }
    if (IsA(node, CurrentOfExpr))
    {
        /* since CurrentOfExpr doesn't carry location, nothing we can do */
        return false;
    }
    /* No extra code needed for PlaceHolderVar; just look in contained expr */
    if (IsA(node, Query))
    {
        /* Recurse into subselects */
        bool        result;
 
        context->sublevels_up++;
        result = query_tree_walker((Query *) node,
                                   locate_var_of_level_walker,
                                   (void *) context,
                                   0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node,
                                  locate_var_of_level_walker,
                                  (void *) context);
}
 
 
/*
 * pull_var_clause
 *    Recursively pulls all Var nodes from an expression clause.
 *
 *    Aggrefs are handled according to these bits in 'flags':
 *      PVC_INCLUDE_AGGREGATES      include Aggrefs in output list
 *      PVC_RECURSE_AGGREGATES      recurse into Aggref arguments
 *      neither flag                throw error if Aggref found
 *    Vars within an Aggref's expression are included in the result only
 *    when PVC_RECURSE_AGGREGATES is specified.
 *
 *    WindowFuncs are handled according to these bits in 'flags':
 *      PVC_INCLUDE_WINDOWFUNCS     include WindowFuncs in output list
 *      PVC_RECURSE_WINDOWFUNCS     recurse into WindowFunc arguments
 *      neither flag                throw error if WindowFunc found
 *    Vars within a WindowFunc's expression are included in the result only
 *    when PVC_RECURSE_WINDOWFUNCS is specified.
 *
 *    PlaceHolderVars are handled according to these bits in 'flags':
 *      PVC_INCLUDE_PLACEHOLDERS    include PlaceHolderVars in output list
 *      PVC_RECURSE_PLACEHOLDERS    recurse into PlaceHolderVar arguments
 *      neither flag                throw error if PlaceHolderVar found
 *    Vars within a PHV's expression are included in the result only
 *    when PVC_RECURSE_PLACEHOLDERS is specified.
 *
 *    GroupingFuncs are treated exactly like Aggrefs, and so do not need
 *    their own flag bits.
 *
 *    CurrentOfExpr nodes are ignored in all cases.
 *
 *    Upper-level vars (with varlevelsup > 0) should not be seen here,
 *    likewise for upper-level Aggrefs and PlaceHolderVars.
 *
 *    Returns list of nodes found.  Note the nodes themselves are not
 *    copied, only referenced.
 *
 * Does not examine subqueries, therefore must only be used after reduction
 * of sublinks to subplans!
 */
List *
pull_var_clause(Node *node, int flags)
{
    pull_var_clause_context context;
 
    /* Assert that caller has not specified inconsistent flags */
    Assert((flags & (PVC_INCLUDE_AGGREGATES | PVC_RECURSE_AGGREGATES))
           != (PVC_INCLUDE_AGGREGATES | PVC_RECURSE_AGGREGATES));
    Assert((flags & (PVC_INCLUDE_WINDOWFUNCS | PVC_RECURSE_WINDOWFUNCS))
           != (PVC_INCLUDE_WINDOWFUNCS | PVC_RECURSE_WINDOWFUNCS));
    Assert((flags & (PVC_INCLUDE_PLACEHOLDERS | PVC_RECURSE_PLACEHOLDERS))
           != (PVC_INCLUDE_PLACEHOLDERS | PVC_RECURSE_PLACEHOLDERS));
 
    context.varlist = NIL;
    context.flags = flags;
 
    pull_var_clause_walker(node, &context);
    return context.varlist;
}
 
static bool
pull_var_clause_walker(Node *node, pull_var_clause_context *context)
{
    if (node == NULL)
        return false;
    if (IsA(node, Var))
    {
        if (((Var *) node)->varlevelsup != 0)
            elog(ERROR, "Upper-level Var found where not expected");
        context->varlist = lappend(context->varlist, node);
        return false;
    }
    else if (IsA(node, Aggref))
    {
        if (((Aggref *) node)->agglevelsup != 0)
            elog(ERROR, "Upper-level Aggref found where not expected");
        if (context->flags & PVC_INCLUDE_AGGREGATES)
        {
            context->varlist = lappend(context->varlist, node);
            /* we do NOT descend into the contained expression */
            return false;
        }
        else if (context->flags & PVC_RECURSE_AGGREGATES)
        {
            /* fall through to recurse into the aggregate's arguments */
        }
        else
            elog(ERROR, "Aggref found where not expected");
    }
    else if (IsA(node, GroupingFunc))
    {
        if (((GroupingFunc *) node)->agglevelsup != 0)
            elog(ERROR, "Upper-level GROUPING found where not expected");
        if (context->flags & PVC_INCLUDE_AGGREGATES)
        {
            context->varlist = lappend(context->varlist, node);
            /* we do NOT descend into the contained expression */
            return false;
        }
        else if (context->flags & PVC_RECURSE_AGGREGATES)
        {
            /* fall through to recurse into the GroupingFunc's arguments */
        }
        else
            elog(ERROR, "GROUPING found where not expected");
    }
    else if (IsA(node, WindowFunc))
    {
        /* WindowFuncs have no levelsup field to check ... */
        if (context->flags & PVC_INCLUDE_WINDOWFUNCS)
        {
            context->varlist = lappend(context->varlist, node);
            /* we do NOT descend into the contained expressions */
            return false;
        }
        else if (context->flags & PVC_RECURSE_WINDOWFUNCS)
        {
            /* fall through to recurse into the windowfunc's arguments */
        }
        else
            elog(ERROR, "WindowFunc found where not expected");
    }
    else if (IsA(node, PlaceHolderVar))
    {
        if (((PlaceHolderVar *) node)->phlevelsup != 0)
            elog(ERROR, "Upper-level PlaceHolderVar found where not expected");
        if (context->flags & PVC_INCLUDE_PLACEHOLDERS)
        {
            context->varlist = lappend(context->varlist, node);
            /* we do NOT descend into the contained expression */
            return false;
        }
        else if (context->flags & PVC_RECURSE_PLACEHOLDERS)
        {
            /* fall through to recurse into the placeholder's expression */
        }
        else
            elog(ERROR, "PlaceHolderVar found where not expected");
    }
    return expression_tree_walker(node, pull_var_clause_walker,
                                  (void *) context);
}
 
 
/*
 * flatten_join_alias_vars
 *    Replace Vars that reference JOIN outputs with references to the original
 *    relation variables instead.  This allows quals involving such vars to be
 *    pushed down.  Whole-row Vars that reference JOIN relations are expanded
 *    into RowExpr constructs that name the individual output Vars.  This
 *    is necessary since we will not scan the JOIN as a base relation, which
 *    is the only way that the executor can directly handle whole-row Vars.
 *
 * This also adjusts relid sets found in some expression node types to
 * substitute the contained base+OJ rels for any join relid.
 *
 * If a JOIN contains sub-selects that have been flattened, its join alias
 * entries might now be arbitrary expressions, not just Vars.  This affects
 * this function in two important ways.  First, we might find ourselves
 * inserting SubLink expressions into subqueries, and we must make sure that
 * their Query.hasSubLinks fields get set to true if so.  If there are any
 * SubLinks in the join alias lists, the outer Query should already have
 * hasSubLinks = true, so this is only relevant to un-flattened subqueries.
 * Second, we have to preserve any varnullingrels info attached to the
 * alias Vars we're replacing.  If the replacement expression is a Var or
 * PlaceHolderVar or constructed from those, we can just add the
 * varnullingrels bits to the existing nullingrels field(s); otherwise
 * we have to add a PlaceHolderVar wrapper.
 *
 * NOTE: this is also used by the parser, to expand join alias Vars before
 * checking GROUP BY validity.  For that use-case, root will be NULL, which
 * is why we have to pass the Query separately.  We need the root itself only
 * for making PlaceHolderVars.  We can avoid making PlaceHolderVars in the
 * parser's usage because it won't be dealing with arbitrary expressions:
 * so long as adjust_standard_join_alias_expression can handle everything
 * the parser would make as a join alias expression, we're OK.
 */
Node *
flatten_join_alias_vars(PlannerInfo *root, Query *query, Node *node)
{
    flatten_join_alias_vars_context context;
 
    /*
     * We do not expect this to be applied to the whole Query, only to
     * expressions or LATERAL subqueries.  Hence, if the top node is a Query,
     * it's okay to immediately increment sublevels_up.
     */
    Assert(node != (Node *) query);
 
    context.root = root;
    context.query = query;
    context.sublevels_up = 0;
    /* flag whether join aliases could possibly contain SubLinks */
    context.possible_sublink = query->hasSubLinks;
    /* if hasSubLinks is already true, no need to work hard */
    context.inserted_sublink = query->hasSubLinks;
 
    return flatten_join_alias_vars_mutator(node, &context);
}
 
static Node *
flatten_join_alias_vars_mutator(Node *node,
                                flatten_join_alias_vars_context *context)
{
    if (node == NULL)
        return NULL;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
        RangeTblEntry *rte;
        Node       *newvar;
 
        /* No change unless Var belongs to a JOIN of the target level */
        if (var->varlevelsup != context->sublevels_up)
            return node;        /* no need to copy, really */
        rte = rt_fetch(var->varno, context->query->rtable);
        if (rte->rtekind != RTE_JOIN)
            return node;
        if (var->varattno == InvalidAttrNumber)
        {
            /* Must expand whole-row reference */
            RowExpr    *rowexpr;
            List       *fields = NIL;
            List       *colnames = NIL;
            ListCell   *lv;
            ListCell   *ln;
 
            Assert(list_length(rte->joinaliasvars) == list_length(rte->eref->colnames));
            forboth(lv, rte->joinaliasvars, ln, rte->eref->colnames)
            {
                newvar = (Node *) lfirst(lv);
                /* Ignore dropped columns */
                if (newvar == NULL)
                    continue;
                newvar = copyObject(newvar);
 
                /*
                 * If we are expanding an alias carried down from an upper
                 * query, must adjust its varlevelsup fields.
                 */
                if (context->sublevels_up != 0)
                    IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);
                /* Preserve original Var's location, if possible */
                if (IsA(newvar, Var))
                    ((Var *) newvar)->location = var->location;
                /* Recurse in case join input is itself a join */
                /* (also takes care of setting inserted_sublink if needed) */
                newvar = flatten_join_alias_vars_mutator(newvar, context);
                fields = lappend(fields, newvar);
                /* We need the names of non-dropped columns, too */
                colnames = lappend(colnames, copyObject((Node *) lfirst(ln)));
            }
            rowexpr = makeNode(RowExpr);
            rowexpr->args = fields;
            rowexpr->row_typeid = var->vartype;
            rowexpr->row_format = COERCE_IMPLICIT_CAST;
            /* vartype will always be RECORDOID, so we always need colnames */
            rowexpr->colnames = colnames;
            rowexpr->location = var->location;
 
            /* Lastly, add any varnullingrels to the replacement expression */
            return add_nullingrels_if_needed(context->root, (Node *) rowexpr,
                                             var);
        }
 
        /* Expand join alias reference */
        Assert(var->varattno > 0);
        newvar = (Node *) list_nth(rte->joinaliasvars, var->varattno - 1);
        Assert(newvar != NULL);
        newvar = copyObject(newvar);
 
        /*
         * If we are expanding an alias carried down from an upper query, must
         * adjust its varlevelsup fields.
         */
        if (context->sublevels_up != 0)
            IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);
 
        /* Preserve original Var's location, if possible */
        if (IsA(newvar, Var))
            ((Var *) newvar)->location = var->location;
 
        /* Recurse in case join input is itself a join */
        newvar = flatten_join_alias_vars_mutator(newvar, context);
 
        /* Detect if we are adding a sublink to query */
        if (context->possible_sublink && !context->inserted_sublink)
            context->inserted_sublink = checkExprHasSubLink(newvar);
 
        /* Lastly, add any varnullingrels to the replacement expression */
        return add_nullingrels_if_needed(context->root, newvar, var);
    }
    if (IsA(node, PlaceHolderVar))
    {
        /* Copy the PlaceHolderVar node with correct mutation of subnodes */
        PlaceHolderVar *phv;
 
        phv = (PlaceHolderVar *) expression_tree_mutator(node,
                                                         flatten_join_alias_vars_mutator,
                                                         (void *) context);
        /* now fix PlaceHolderVar's relid sets */
        if (phv->phlevelsup == context->sublevels_up)
        {
            phv->phrels = alias_relid_set(context->query,
                                          phv->phrels);
            /* we *don't* change phnullingrels */
        }
        return (Node *) phv;
    }
 
    if (IsA(node, Query))
    {
        /* Recurse into RTE subquery or not-yet-planned sublink subquery */
        Query      *newnode;
        bool        save_inserted_sublink;
 
        context->sublevels_up++;
        save_inserted_sublink = context->inserted_sublink;
        context->inserted_sublink = ((Query *) node)->hasSubLinks;
        newnode = query_tree_mutator((Query *) node,
                                     flatten_join_alias_vars_mutator,
                                     (void *) context,
                                     QTW_IGNORE_JOINALIASES);
        newnode->hasSubLinks |= context->inserted_sublink;
        context->inserted_sublink = save_inserted_sublink;
        context->sublevels_up--;
        return (Node *) newnode;
    }
    /* Already-planned tree not supported */
    Assert(!IsA(node, SubPlan));
    Assert(!IsA(node, AlternativeSubPlan));
    /* Shouldn't need to handle these planner auxiliary nodes here */
    Assert(!IsA(node, SpecialJoinInfo));
    Assert(!IsA(node, PlaceHolderInfo));
    Assert(!IsA(node, MinMaxAggInfo));
 
    return expression_tree_mutator(node, flatten_join_alias_vars_mutator,
                                   (void *) context);
}
 
/*
 * flatten_group_exprs
 *    Replace Vars that reference GROUP outputs with the underlying grouping
 *    expressions.
 *
 * We have to preserve any varnullingrels info attached to the group Vars we're
 * replacing.  If the replacement expression is a Var or PlaceHolderVar or
 * constructed from those, we can just add the varnullingrels bits to the
 * existing nullingrels field(s); otherwise we have to add a PlaceHolderVar
 * wrapper.
 *
 * NOTE: this is also used by ruleutils.c, to deparse one query parsetree back
 * to source text.  For that use-case, root will be NULL, which is why we have
 * to pass the Query separately.  We need the root itself only for preserving
 * varnullingrels.  We can avoid preserving varnullingrels in the ruleutils.c's
 * usage because it does not make any difference to the deparsed source text.
 */
Node *
flatten_group_exprs(PlannerInfo *root, Query *query, Node *node)
{
    flatten_join_alias_vars_context context;
 
    /*
     * We do not expect this to be applied to the whole Query, only to
     * expressions or LATERAL subqueries.  Hence, if the top node is a Query,
     * it's okay to immediately increment sublevels_up.
     */
    Assert(node != (Node *) query);
 
    context.root = root;
    context.query = query;
    context.sublevels_up = 0;
    /* flag whether grouping expressions could possibly contain SubLinks */
    context.possible_sublink = query->hasSubLinks;
    /* if hasSubLinks is already true, no need to work hard */
    context.inserted_sublink = query->hasSubLinks;
 
    return flatten_group_exprs_mutator(node, &context);
}
 
static Node *
flatten_group_exprs_mutator(Node *node,
                            flatten_join_alias_vars_context *context)
{
    if (node == NULL)
        return NULL;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
        RangeTblEntry *rte;
        Node       *newvar;
 
        /* No change unless Var belongs to the GROUP of the target level */
        if (var->varlevelsup != context->sublevels_up)
            return node;        /* no need to copy, really */
        rte = rt_fetch(var->varno, context->query->rtable);
        if (rte->rtekind != RTE_GROUP)
            return node;
 
        /* Expand group exprs reference */
        Assert(var->varattno > 0);
        newvar = (Node *) list_nth(rte->groupexprs, var->varattno - 1);
        Assert(newvar != NULL);
        newvar = copyObject(newvar);
 
        /*
         * If we are expanding an expr carried down from an upper query, must
         * adjust its varlevelsup fields.
         */
        if (context->sublevels_up != 0)
            IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);
 
        /* Preserve original Var's location, if possible */
        if (IsA(newvar, Var))
            ((Var *) newvar)->location = var->location;
 
        /* Detect if we are adding a sublink to query */
        if (context->possible_sublink && !context->inserted_sublink)
            context->inserted_sublink = checkExprHasSubLink(newvar);
 
        /* Lastly, add any varnullingrels to the replacement expression */
        return mark_nullable_by_grouping(context->root, newvar, var);
    }
 
    if (IsA(node, Aggref))
    {
        Aggref     *agg = (Aggref *) node;
 
        if ((int) agg->agglevelsup == context->sublevels_up)
        {
            /*
             * If we find an aggregate call of the original level, do not
             * recurse into its normal arguments, ORDER BY arguments, or
             * filter; there are no grouped vars there.  But we should check
             * direct arguments as though they weren't in an aggregate.
             */
            agg = copyObject(agg);
            agg->aggdirectargs = (List *)
                flatten_group_exprs_mutator((Node *) agg->aggdirectargs, context);
 
            return (Node *) agg;
        }
 
        /*
         * We can skip recursing into aggregates of higher levels altogether,
         * since they could not possibly contain Vars of concern to us (see
         * transformAggregateCall).  We do need to look at aggregates of lower
         * levels, however.
         */
        if ((int) agg->agglevelsup > context->sublevels_up)
            return node;
    }
 
    if (IsA(node, GroupingFunc))
    {
        GroupingFunc *grp = (GroupingFunc *) node;
 
        /*
         * If we find a GroupingFunc node of the original or higher level, do
         * not recurse into its arguments; there are no grouped vars there.
         */
        if ((int) grp->agglevelsup >= context->sublevels_up)
            return node;
    }
 
    if (IsA(node, Query))
    {
        /* Recurse into RTE subquery or not-yet-planned sublink subquery */
        Query      *newnode;
        bool        save_inserted_sublink;
 
        context->sublevels_up++;
        save_inserted_sublink = context->inserted_sublink;
        context->inserted_sublink = ((Query *) node)->hasSubLinks;
        newnode = query_tree_mutator((Query *) node,
                                     flatten_group_exprs_mutator,
                                     (void *) context,
                                     QTW_IGNORE_GROUPEXPRS);
        newnode->hasSubLinks |= context->inserted_sublink;
        context->inserted_sublink = save_inserted_sublink;
        context->sublevels_up--;
        return (Node *) newnode;
    }
 
    return expression_tree_mutator(node, flatten_group_exprs_mutator,
                                   (void *) context);
}
 
/*
 * Add oldvar's varnullingrels, if any, to a flattened grouping expression.
 * The newnode has been copied, so we can modify it freely.
 */
static Node *
mark_nullable_by_grouping(PlannerInfo *root, Node *newnode, Var *oldvar)
{
    Relids      relids;
 
    if (root == NULL)
        return newnode;
    if (oldvar->varnullingrels == NULL)
        return newnode;         /* nothing to do */
 
    Assert(bms_equal(oldvar->varnullingrels,
                     bms_make_singleton(root->group_rtindex)));
 
    relids = pull_varnos_of_level(root, newnode, oldvar->varlevelsup);
 
    if (!bms_is_empty(relids))
    {
        /*
         * If the newnode is not variable-free, we set the nullingrels of Vars
         * or PHVs that are contained in the expression.  This is not really
         * 'correct' in theory, because it is the whole expression that can be
         * nullable by grouping sets, not its individual vars.  But it works
         * in practice, because what we need is that the expression can be
         * somehow distinguished from the same expression in ECs, and marking
         * its vars is sufficient for this purpose.
         */
        newnode = add_nulling_relids(newnode,
                                     relids,
                                     oldvar->varnullingrels);
    }
    else                        /* variable-free? */
    {
        /*
         * If the newnode is variable-free and does not contain volatile
         * functions or set-returning functions, it can be treated as a member
         * of EC that is redundant.  So wrap it in a new PlaceHolderVar to
         * carry the nullingrels.  Otherwise we do not bother to make any
         * changes.
         *
         * Aggregate functions and window functions are not allowed in
         * grouping expressions.
         */
        Assert(!contain_agg_clause(newnode));
        Assert(!contain_window_function(newnode));
 
        if (!contain_volatile_functions(newnode) &&
            !expression_returns_set(newnode))
        {
            PlaceHolderVar *newphv;
            Relids      phrels;
 
            phrels = get_relids_in_jointree((Node *) root->parse->jointree,
                                            true, false);
            Assert(!bms_is_empty(phrels));
 
            newphv = make_placeholder_expr(root, (Expr *) newnode, phrels);
            /* newphv has zero phlevelsup and NULL phnullingrels; fix it */
            newphv->phlevelsup = oldvar->varlevelsup;
            newphv->phnullingrels = bms_copy(oldvar->varnullingrels);
            newnode = (Node *) newphv;
        }
    }
 
    return newnode;
}
 
/*
 * Add oldvar's varnullingrels, if any, to a flattened join alias expression.
 * The newnode has been copied, so we can modify it freely.
 */
static Node *
add_nullingrels_if_needed(PlannerInfo *root, Node *newnode, Var *oldvar)
{
    if (oldvar->varnullingrels == NULL)
        return newnode;         /* nothing to do */
    /* If possible, do it by adding to existing nullingrel fields */
    if (is_standard_join_alias_expression(newnode, oldvar))
        adjust_standard_join_alias_expression(newnode, oldvar);
    else if (root)
    {
        /*
         * We can insert a PlaceHolderVar to carry the nullingrels.  However,
         * deciding where to evaluate the PHV is slightly tricky.  We first
         * try to evaluate it at the natural semantic level of the new
         * expression; but if that expression is variable-free, fall back to
         * evaluating it at the join that the oldvar is an alias Var for.
         */
        PlaceHolderVar *newphv;
        Index       levelsup = oldvar->varlevelsup;
        Relids      phrels = pull_varnos_of_level(root, newnode, levelsup);
 
        if (bms_is_empty(phrels))   /* variable-free? */
        {
            if (levelsup != 0)  /* this won't work otherwise */
                elog(ERROR, "unsupported join alias expression");
            phrels = get_relids_for_join(root->parse, oldvar->varno);
            /* If it's an outer join, eval below not above the join */
            phrels = bms_del_member(phrels, oldvar->varno);
            Assert(!bms_is_empty(phrels));
        }
        newphv = make_placeholder_expr(root, (Expr *) newnode, phrels);
        /* newphv has zero phlevelsup and NULL phnullingrels; fix it */
        newphv->phlevelsup = levelsup;
        newphv->phnullingrels = bms_copy(oldvar->varnullingrels);
        newnode = (Node *) newphv;
    }
    else
    {
        /* ooops, we're missing support for something the parser can make */
        elog(ERROR, "unsupported join alias expression");
    }
    return newnode;
}
 
/*
 * Check to see if we can insert nullingrels into this join alias expression
 * without use of a separate PlaceHolderVar.
 *
 * This will handle Vars, PlaceHolderVars, and implicit-coercion and COALESCE
 * expressions built from those.  This coverage needs to handle anything
 * that the parser would put into joinaliasvars.
 */
static bool
is_standard_join_alias_expression(Node *newnode, Var *oldvar)
{
    if (newnode == NULL)
        return false;
    if (IsA(newnode, Var) &&
        ((Var *) newnode)->varlevelsup == oldvar->varlevelsup)
        return true;
    else if (IsA(newnode, PlaceHolderVar) &&
             ((PlaceHolderVar *) newnode)->phlevelsup == oldvar->varlevelsup)
        return true;
    else if (IsA(newnode, FuncExpr))
    {
        FuncExpr   *fexpr = (FuncExpr *) newnode;
 
        /*
         * We need to assume that the function wouldn't produce non-NULL from
         * NULL, which is reasonable for implicit coercions but otherwise not
         * so much.  (Looking at its strictness is likely overkill, and anyway
         * it would cause us to fail if someone forgot to mark an implicit
         * coercion as strict.)
         */
        if (fexpr->funcformat != COERCE_IMPLICIT_CAST ||
            fexpr->args == NIL)
            return false;
 
        /*
         * Examine only the first argument --- coercions might have additional
         * arguments that are constants.
         */
        return is_standard_join_alias_expression(linitial(fexpr->args), oldvar);
    }
    else if (IsA(newnode, RelabelType))
    {
        RelabelType *relabel = (RelabelType *) newnode;
 
        /* This definitely won't produce non-NULL from NULL */
        return is_standard_join_alias_expression((Node *) relabel->arg, oldvar);
    }
    else if (IsA(newnode, CoerceViaIO))
    {
        CoerceViaIO *iocoerce = (CoerceViaIO *) newnode;
 
        /* This definitely won't produce non-NULL from NULL */
        return is_standard_join_alias_expression((Node *) iocoerce->arg, oldvar);
    }
    else if (IsA(newnode, ArrayCoerceExpr))
    {
        ArrayCoerceExpr *acoerce = (ArrayCoerceExpr *) newnode;
 
        /* This definitely won't produce non-NULL from NULL (at array level) */
        return is_standard_join_alias_expression((Node *) acoerce->arg, oldvar);
    }
    else if (IsA(newnode, CoalesceExpr))
    {
        CoalesceExpr *cexpr = (CoalesceExpr *) newnode;
        ListCell   *lc;
 
        Assert(cexpr->args != NIL);
        foreach(lc, cexpr->args)
        {
            if (!is_standard_join_alias_expression(lfirst(lc), oldvar))
                return false;
        }
        return true;
    }
    else
        return false;
}
 
/*
 * Insert nullingrels into an expression accepted by
 * is_standard_join_alias_expression.
 */
static void
adjust_standard_join_alias_expression(Node *newnode, Var *oldvar)
{
    if (IsA(newnode, Var) &&
        ((Var *) newnode)->varlevelsup == oldvar->varlevelsup)
    {
        Var        *newvar = (Var *) newnode;
 
        newvar->varnullingrels = bms_add_members(newvar->varnullingrels,
                                                 oldvar->varnullingrels);
    }
    else if (IsA(newnode, PlaceHolderVar) &&
             ((PlaceHolderVar *) newnode)->phlevelsup == oldvar->varlevelsup)
    {
        PlaceHolderVar *newphv = (PlaceHolderVar *) newnode;
 
        newphv->phnullingrels = bms_add_members(newphv->phnullingrels,
                                                oldvar->varnullingrels);
    }
    else if (IsA(newnode, FuncExpr))
    {
        FuncExpr   *fexpr = (FuncExpr *) newnode;
 
        adjust_standard_join_alias_expression(linitial(fexpr->args), oldvar);
    }
    else if (IsA(newnode, RelabelType))
    {
        RelabelType *relabel = (RelabelType *) newnode;
 
        adjust_standard_join_alias_expression((Node *) relabel->arg, oldvar);
    }
    else if (IsA(newnode, CoerceViaIO))
    {
        CoerceViaIO *iocoerce = (CoerceViaIO *) newnode;
 
        adjust_standard_join_alias_expression((Node *) iocoerce->arg, oldvar);
    }
    else if (IsA(newnode, ArrayCoerceExpr))
    {
        ArrayCoerceExpr *acoerce = (ArrayCoerceExpr *) newnode;
 
        adjust_standard_join_alias_expression((Node *) acoerce->arg, oldvar);
    }
    else if (IsA(newnode, CoalesceExpr))
    {
        CoalesceExpr *cexpr = (CoalesceExpr *) newnode;
        ListCell   *lc;
 
        Assert(cexpr->args != NIL);
        foreach(lc, cexpr->args)
        {
            adjust_standard_join_alias_expression(lfirst(lc), oldvar);
        }
    }
    else
        Assert(false);
}
 
/*
 * alias_relid_set: in a set of RT indexes, replace joins by their
 * underlying base+OJ relids
 */
static Relids
alias_relid_set(Query *query, Relids relids)
{
    Relids      result = NULL;
    int         rtindex;
 
    rtindex = -1;
    while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
    {
        RangeTblEntry *rte = rt_fetch(rtindex, query->rtable);
 
        if (rte->rtekind == RTE_JOIN)
            result = bms_join(result, get_relids_for_join(query, rtindex));
        else
            result = bms_add_member(result, rtindex);
    }
    return result;
}