primnodes.h

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/*-------------------------------------------------------------------------
 *
 * primnodes.h
 *    Definitions for "primitive" node types, those that are used in more
 *    than one of the parse/plan/execute stages of the query pipeline.
 *    Currently, these are mostly nodes for executable expressions
 *    and join trees.
 *
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/nodes/primnodes.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef PRIMNODES_H
#define PRIMNODES_H

#include "access/attnum.h"
#include "nodes/bitmapset.h"
#include "nodes/pg_list.h"


/* ----------------------------------------------------------------
 *                      node definitions
 * ----------------------------------------------------------------
 */

/*
 * Alias -
 *    specifies an alias for a range variable; the alias might also
 *    specify renaming of columns within the table.
 *
 * Note: colnames is a list of Value nodes (always strings).  In Alias structs
 * associated with RTEs, there may be entries corresponding to dropped
 * columns; these are normally empty strings ("").  See parsenodes.h for info.
 */
typedef struct Alias
{
    NodeTag     type;
    char       *aliasname;      /* aliased rel name (never qualified) */
    List       *colnames;       /* optional list of column aliases */
} Alias;

/* What to do at commit time for temporary relations */
typedef enum OnCommitAction
{
    ONCOMMIT_NOOP,              /* No ON COMMIT clause (do nothing) */
    ONCOMMIT_PRESERVE_ROWS,     /* ON COMMIT PRESERVE ROWS (do nothing) */
    ONCOMMIT_DELETE_ROWS,       /* ON COMMIT DELETE ROWS */
    ONCOMMIT_DROP               /* ON COMMIT DROP */
} OnCommitAction;

/*
 * RangeVar - range variable, used in FROM clauses
 *
 * Also used to represent table names in utility statements; there, the alias
 * field is not used, and inh tells whether to apply the operation
 * recursively to child tables.  In some contexts it is also useful to carry
 * a TEMP table indication here.
 */
typedef struct RangeVar
{
    NodeTag     type;
    char       *catalogname;    /* the catalog (database) name, or NULL */
    char       *schemaname;     /* the schema name, or NULL */
    char       *relname;        /* the relation/sequence name */
    bool        inh;            /* expand rel by inheritance? recursively act
                                 * on children? */
    char        relpersistence; /* see RELPERSISTENCE_* in pg_class.h */
    Alias      *alias;          /* table alias & optional column aliases */
    int         location;       /* token location, or -1 if unknown */
} RangeVar;

/*
 * TableFunc - node for a table function, such as XMLTABLE.
 *
 * Entries in the ns_names list are either string Value nodes containing
 * literal namespace names, or NULL pointers to represent DEFAULT.
 */
typedef struct TableFunc
{
    NodeTag     type;
    List       *ns_uris;        /* list of namespace URI expressions */
    List       *ns_names;       /* list of namespace names or NULL */
    Node       *docexpr;        /* input document expression */
    Node       *rowexpr;        /* row filter expression */
    List       *colnames;       /* column names (list of String) */
    List       *coltypes;       /* OID list of column type OIDs */
    List       *coltypmods;     /* integer list of column typmods */
    List       *colcollations;  /* OID list of column collation OIDs */
    List       *colexprs;       /* list of column filter expressions */
    List       *coldefexprs;    /* list of column default expressions */
    Bitmapset  *notnulls;       /* nullability flag for each output column */
    int         ordinalitycol;  /* counts from 0; -1 if none specified */
    int         location;       /* token location, or -1 if unknown */
} TableFunc;

/*
 * IntoClause - target information for SELECT INTO, CREATE TABLE AS, and
 * CREATE MATERIALIZED VIEW
 *
 * For CREATE MATERIALIZED VIEW, viewQuery is the parsed-but-not-rewritten
 * SELECT Query for the view; otherwise it's NULL.  (Although it's actually
 * Query*, we declare it as Node* to avoid a forward reference.)
 */
typedef struct IntoClause
{
    NodeTag     type;

    RangeVar   *rel;            /* target relation name */
    List       *colNames;       /* column names to assign, or NIL */
    char       *accessMethod;   /* table access method */
    List       *options;        /* options from WITH clause */
    OnCommitAction onCommit;    /* what do we do at COMMIT? */
    char       *tableSpaceName; /* table space to use, or NULL */
    Node       *viewQuery;      /* materialized view's SELECT query */
    bool        skipData;       /* true for WITH NO DATA */
} IntoClause;


/* ----------------------------------------------------------------
 *                  node types for executable expressions
 * ----------------------------------------------------------------
 */

/*
 * Expr - generic superclass for executable-expression nodes
 *
 * All node types that are used in executable expression trees should derive
 * from Expr (that is, have Expr as their first field).  Since Expr only
 * contains NodeTag, this is a formality, but it is an easy form of
 * documentation.  See also the ExprState node types in execnodes.h.
 */
typedef struct Expr
{
    NodeTag     type;
} Expr;

/*
 * Var - expression node representing a variable (ie, a table column)
 *
 * In the parser and planner, varno and varattno identify the semantic
 * referent, which is a base-relation column unless the reference is to a join
 * USING column that isn't semantically equivalent to either join input column
 * (because it is a FULL join or the input column requires a type coercion).
 * In those cases varno and varattno refer to the JOIN RTE.  (Early in the
 * planner, we replace such join references by the implied expression; but up
 * till then we want join reference Vars to keep their original identity for
 * query-printing purposes.)
 *
 * At the end of planning, Var nodes appearing in upper-level plan nodes are
 * reassigned to point to the outputs of their subplans; for example, in a
 * join node varno becomes INNER_VAR or OUTER_VAR and varattno becomes the
 * index of the proper element of that subplan's target list.  Similarly,
 * INDEX_VAR is used to identify Vars that reference an index column rather
 * than a heap column.  (In ForeignScan and CustomScan plan nodes, INDEX_VAR
 * is abused to signify references to columns of a custom scan tuple type.)
 *
 * In the parser, varnosyn and varattnosyn are either identical to
 * varno/varattno, or they specify the column's position in an aliased JOIN
 * RTE that hides the semantic referent RTE's refname.  This is a syntactic
 * identifier as opposed to the semantic identifier; it tells ruleutils.c
 * how to print the Var properly.  varnosyn/varattnosyn retain their values
 * throughout planning and execution, so they are particularly helpful to
 * identify Vars when debugging.  Note, however, that a Var that is generated
 * in the planner and doesn't correspond to any simple relation column may
 * have varnosyn = varattnosyn = 0.
 */
#define    INNER_VAR        65000   /* reference to inner subplan */
#define    OUTER_VAR        65001   /* reference to outer subplan */
#define    INDEX_VAR        65002   /* reference to index column */

#define IS_SPECIAL_VARNO(varno)     ((varno) >= INNER_VAR)

/* Symbols for the indexes of the special RTE entries in rules */
#define    PRS2_OLD_VARNO           1
#define    PRS2_NEW_VARNO           2

typedef struct Var
{
    Expr        xpr;
    Index       varno;          /* index of this var's relation in the range
                                 * table, or INNER_VAR/OUTER_VAR/INDEX_VAR */
    AttrNumber  varattno;       /* attribute number of this var, or zero for
                                 * all attrs ("whole-row Var") */
    Oid         vartype;        /* pg_type OID for the type of this var */
    int32       vartypmod;      /* pg_attribute typmod value */
    Oid         varcollid;      /* OID of collation, or InvalidOid if none */
    Index       varlevelsup;    /* for subquery variables referencing outer
                                 * relations; 0 in a normal var, >0 means N
                                 * levels up */
    Index       varnosyn;       /* syntactic relation index (0 if unknown) */
    AttrNumber  varattnosyn;    /* syntactic attribute number */
    int         location;       /* token location, or -1 if unknown */
} Var;

/*
 * Const
 *
 * Note: for varlena data types, we make a rule that a Const node's value
 * must be in non-extended form (4-byte header, no compression or external
 * references).  This ensures that the Const node is self-contained and makes
 * it more likely that equal() will see logically identical values as equal.
 */
typedef struct Const
{
    Expr        xpr;
    Oid         consttype;      /* pg_type OID of the constant's datatype */
    int32       consttypmod;    /* typmod value, if any */
    Oid         constcollid;    /* OID of collation, or InvalidOid if none */
    int         constlen;       /* typlen of the constant's datatype */
    Datum       constvalue;     /* the constant's value */
    bool        constisnull;    /* whether the constant is null (if true,
                                 * constvalue is undefined) */
    bool        constbyval;     /* whether this datatype is passed by value.
                                 * If true, then all the information is stored
                                 * in the Datum. If false, then the Datum
                                 * contains a pointer to the information. */
    int         location;       /* token location, or -1 if unknown */
} Const;

/*
 * Param
 *
 *      paramkind specifies the kind of parameter. The possible values
 *      for this field are:
 *
 *      PARAM_EXTERN:  The parameter value is supplied from outside the plan.
 *              Such parameters are numbered from 1 to n.
 *
 *      PARAM_EXEC:  The parameter is an internal executor parameter, used
 *              for passing values into and out of sub-queries or from
 *              nestloop joins to their inner scans.
 *              For historical reasons, such parameters are numbered from 0.
 *              These numbers are independent of PARAM_EXTERN numbers.
 *
 *      PARAM_SUBLINK:  The parameter represents an output column of a SubLink
 *              node's sub-select.  The column number is contained in the
 *              `paramid' field.  (This type of Param is converted to
 *              PARAM_EXEC during planning.)
 *
 *      PARAM_MULTIEXPR:  Like PARAM_SUBLINK, the parameter represents an
 *              output column of a SubLink node's sub-select, but here, the
 *              SubLink is always a MULTIEXPR SubLink.  The high-order 16 bits
 *              of the `paramid' field contain the SubLink's subLinkId, and
 *              the low-order 16 bits contain the column number.  (This type
 *              of Param is also converted to PARAM_EXEC during planning.)
 */
typedef enum ParamKind
{
    PARAM_EXTERN,
    PARAM_EXEC,
    PARAM_SUBLINK,
    PARAM_MULTIEXPR
} ParamKind;

typedef struct Param
{
    Expr        xpr;
    ParamKind   paramkind;      /* kind of parameter. See above */
    int         paramid;        /* numeric ID for parameter */
    Oid         paramtype;      /* pg_type OID of parameter's datatype */
    int32       paramtypmod;    /* typmod value, if known */
    Oid         paramcollid;    /* OID of collation, or InvalidOid if none */
    int         location;       /* token location, or -1 if unknown */
} Param;

/*
 * Aggref
 *
 * The aggregate's args list is a targetlist, ie, a list of TargetEntry nodes.
 *
 * For a normal (non-ordered-set) aggregate, the non-resjunk TargetEntries
 * represent the aggregate's regular arguments (if any) and resjunk TLEs can
 * be added at the end to represent ORDER BY expressions that are not also
 * arguments.  As in a top-level Query, the TLEs can be marked with
 * ressortgroupref indexes to let them be referenced by SortGroupClause
 * entries in the aggorder and/or aggdistinct lists.  This represents ORDER BY
 * and DISTINCT operations to be applied to the aggregate input rows before
 * they are passed to the transition function.  The grammar only allows a
 * simple "DISTINCT" specifier for the arguments, but we use the full
 * query-level representation to allow more code sharing.
 *
 * For an ordered-set aggregate, the args list represents the WITHIN GROUP
 * (aggregated) arguments, all of which will be listed in the aggorder list.
 * DISTINCT is not supported in this case, so aggdistinct will be NIL.
 * The direct arguments appear in aggdirectargs (as a list of plain
 * expressions, not TargetEntry nodes).
 *
 * aggtranstype is the data type of the state transition values for this
 * aggregate (resolved to an actual type, if agg's transtype is polymorphic).
 * This is determined during planning and is InvalidOid before that.
 *
 * aggargtypes is an OID list of the data types of the direct and regular
 * arguments.  Normally it's redundant with the aggdirectargs and args lists,
 * but in a combining aggregate, it's not because the args list has been
 * replaced with a single argument representing the partial-aggregate
 * transition values.
 *
 * aggsplit indicates the expected partial-aggregation mode for the Aggref's
 * parent plan node.  It's always set to AGGSPLIT_SIMPLE in the parser, but
 * the planner might change it to something else.  We use this mainly as
 * a crosscheck that the Aggrefs match the plan; but note that when aggsplit
 * indicates a non-final mode, aggtype reflects the transition data type
 * not the SQL-level output type of the aggregate.
 *
 * aggno and aggtransno are -1 in the parse stage, and are set in planning.
 * Aggregates with the same 'aggno' represent the same aggregate expression,
 * and can share the result.  Aggregates with same 'transno' but different
 * 'aggno' can share the same transition state, only the final function needs
 * to be called separately.
 */
typedef struct Aggref
{
    Expr        xpr;
    Oid         aggfnoid;       /* pg_proc Oid of the aggregate */
    Oid         aggtype;        /* type Oid of result of the aggregate */
    Oid         aggcollid;      /* OID of collation of result */
    Oid         inputcollid;    /* OID of collation that function should use */
    Oid         aggtranstype;   /* type Oid of aggregate's transition value */
    List       *aggargtypes;    /* type Oids of direct and aggregated args */
    List       *aggdirectargs;  /* direct arguments, if an ordered-set agg */
    List       *args;           /* aggregated arguments and sort expressions */
    List       *aggorder;       /* ORDER BY (list of SortGroupClause) */
    List       *aggdistinct;    /* DISTINCT (list of SortGroupClause) */
    Expr       *aggfilter;      /* FILTER expression, if any */
    bool        aggstar;        /* true if argument list was really '*' */
    bool        aggvariadic;    /* true if variadic arguments have been
                                 * combined into an array last argument */
    char        aggkind;        /* aggregate kind (see pg_aggregate.h) */
    Index       agglevelsup;    /* > 0 if agg belongs to outer query */
    AggSplit    aggsplit;       /* expected agg-splitting mode of parent Agg */
    int         aggno;          /* unique ID within the Agg node */
    int         aggtransno;     /* unique ID of transition state in the Agg */
    int         location;       /* token location, or -1 if unknown */
} Aggref;

/*
 * GroupingFunc
 *
 * A GroupingFunc is a GROUPING(...) expression, which behaves in many ways
 * like an aggregate function (e.g. it "belongs" to a specific query level,
 * which might not be the one immediately containing it), but also differs in
 * an important respect: it never evaluates its arguments, they merely
 * designate expressions from the GROUP BY clause of the query level to which
 * it belongs.
 *
 * The spec defines the evaluation of GROUPING() purely by syntactic
 * replacement, but we make it a real expression for optimization purposes so
 * that one Agg node can handle multiple grouping sets at once.  Evaluating the
 * result only needs the column positions to check against the grouping set
 * being projected.  However, for EXPLAIN to produce meaningful output, we have
 * to keep the original expressions around, since expression deparse does not
 * give us any feasible way to get at the GROUP BY clause.
 *
 * Also, we treat two GroupingFunc nodes as equal if they have equal arguments
 * lists and agglevelsup, without comparing the refs and cols annotations.
 *
 * In raw parse output we have only the args list; parse analysis fills in the
 * refs list, and the planner fills in the cols list.
 */
typedef struct GroupingFunc
{
    Expr        xpr;
    List       *args;           /* arguments, not evaluated but kept for
                                 * benefit of EXPLAIN etc. */
    List       *refs;           /* ressortgrouprefs of arguments */
    List       *cols;           /* actual column positions set by planner */
    Index       agglevelsup;    /* same as Aggref.agglevelsup */
    int         location;       /* token location */
} GroupingFunc;

/*
 * WindowFunc
 */
typedef struct WindowFunc
{
    Expr        xpr;
    Oid         winfnoid;       /* pg_proc Oid of the function */
    Oid         wintype;        /* type Oid of result of the window function */
    Oid         wincollid;      /* OID of collation of result */
    Oid         inputcollid;    /* OID of collation that function should use */
    List       *args;           /* arguments to the window function */
    Expr       *aggfilter;      /* FILTER expression, if any */
    Index       winref;         /* index of associated WindowClause */
    bool        winstar;        /* true if argument list was really '*' */
    bool        winagg;         /* is function a simple aggregate? */
    int         location;       /* token location, or -1 if unknown */
} WindowFunc;

/*
 * SubscriptingRef: describes a subscripting operation over a container
 * (array, etc).
 *
 * A SubscriptingRef can describe fetching a single element from a container,
 * fetching a part of a container (e.g. an array slice), storing a single
 * element into a container, or storing a slice.  The "store" cases work with
 * an initial container value and a source value that is inserted into the
 * appropriate part of the container; the result of the operation is an
 * entire new modified container value.
 *
 * If reflowerindexpr = NIL, then we are fetching or storing a single container
 * element at the subscripts given by refupperindexpr. Otherwise we are
 * fetching or storing a container slice, that is a rectangular subcontainer
 * with lower and upper bounds given by the index expressions.
 * reflowerindexpr must be the same length as refupperindexpr when it
 * is not NIL.
 *
 * In the slice case, individual expressions in the subscript lists can be
 * NULL, meaning "substitute the array's current lower or upper bound".
 * (Non-array containers may or may not support this.)
 *
 * refcontainertype is the actual container type that determines the
 * subscripting semantics.  (This will generally be either the exposed type of
 * refexpr, or the base type if that is a domain.)  refelemtype is the type of
 * the container's elements; this is saved for the use of the subscripting
 * functions, but is not used by the core code.  refrestype, reftypmod, and
 * refcollid describe the type of the SubscriptingRef's result.  In a store
 * expression, refrestype will always match refcontainertype; in a fetch,
 * it could be refelemtype for an element fetch, or refcontainertype for a
 * slice fetch, or possibly something else as determined by type-specific
 * subscripting logic.  Likewise, reftypmod and refcollid will match the
 * container's properties in a store, but could be different in a fetch.
 *
 * Note: for the cases where a container is returned, if refexpr yields a R/W
 * expanded container, then the implementation is allowed to modify that
 * object in-place and return the same object.
 */
typedef struct SubscriptingRef
{
    Expr        xpr;
    Oid         refcontainertype;   /* type of the container proper */
    Oid         refelemtype;    /* the container type's pg_type.typelem */
    Oid         refrestype;     /* type of the SubscriptingRef's result */
    int32       reftypmod;      /* typmod of the result */
    Oid         refcollid;      /* collation of result, or InvalidOid if none */
    List       *refupperindexpr;    /* expressions that evaluate to upper
                                     * container indexes */
    List       *reflowerindexpr;    /* expressions that evaluate to lower
                                     * container indexes, or NIL for single
                                     * container element */
    Expr       *refexpr;        /* the expression that evaluates to a
                                 * container value */
    Expr       *refassgnexpr;   /* expression for the source value, or NULL if
                                 * fetch */
} SubscriptingRef;

/*
 * CoercionContext - distinguishes the allowed set of type casts
 *
 * NB: ordering of the alternatives is significant; later (larger) values
 * allow more casts than earlier ones.
 */
typedef enum CoercionContext
{
    COERCION_IMPLICIT,          /* coercion in context of expression */
    COERCION_ASSIGNMENT,        /* coercion in context of assignment */
    COERCION_PLPGSQL,           /* if no assignment cast, use CoerceViaIO */
    COERCION_EXPLICIT           /* explicit cast operation */
} CoercionContext;

/*
 * CoercionForm - how to display a FuncExpr or related node
 *
 * "Coercion" is a bit of a misnomer, since this value records other
 * special syntaxes besides casts, but for now we'll keep this naming.
 *
 * NB: equal() ignores CoercionForm fields, therefore this *must* not carry
 * any semantically significant information.  We need that behavior so that
 * the planner will consider equivalent implicit and explicit casts to be
 * equivalent.  In cases where those actually behave differently, the coercion
 * function's arguments will be different.
 */
typedef enum CoercionForm
{
    COERCE_EXPLICIT_CALL,       /* display as a function call */
    COERCE_EXPLICIT_CAST,       /* display as an explicit cast */
    COERCE_IMPLICIT_CAST,       /* implicit cast, so hide it */
    COERCE_SQL_SYNTAX           /* display with SQL-mandated special syntax */
} CoercionForm;

/*
 * FuncExpr - expression node for a function call
 */
typedef struct FuncExpr
{
    Expr        xpr;
    Oid         funcid;         /* PG_PROC OID of the function */
    Oid         funcresulttype; /* PG_TYPE OID of result value */
    bool        funcretset;     /* true if function returns set */
    bool        funcvariadic;   /* true if variadic arguments have been
                                 * combined into an array last argument */
    CoercionForm funcformat;    /* how to display this function call */
    Oid         funccollid;     /* OID of collation of result */
    Oid         inputcollid;    /* OID of collation that function should use */
    List       *args;           /* arguments to the function */
    int         location;       /* token location, or -1 if unknown */
} FuncExpr;

/*
 * NamedArgExpr - a named argument of a function
 *
 * This node type can only appear in the args list of a FuncCall or FuncExpr
 * node.  We support pure positional call notation (no named arguments),
 * named notation (all arguments are named), and mixed notation (unnamed
 * arguments followed by named ones).
 *
 * Parse analysis sets argnumber to the positional index of the argument,
 * but doesn't rearrange the argument list.
 *
 * The planner will convert argument lists to pure positional notation
 * during expression preprocessing, so execution never sees a NamedArgExpr.
 */
typedef struct NamedArgExpr
{
    Expr        xpr;
    Expr       *arg;            /* the argument expression */
    char       *name;           /* the name */
    int         argnumber;      /* argument's number in positional notation */
    int         location;       /* argument name location, or -1 if unknown */
} NamedArgExpr;

/*
 * OpExpr - expression node for an operator invocation
 *
 * Semantically, this is essentially the same as a function call.
 *
 * Note that opfuncid is not necessarily filled in immediately on creation
 * of the node.  The planner makes sure it is valid before passing the node
 * tree to the executor, but during parsing/planning opfuncid can be 0.
 */
typedef struct OpExpr
{
    Expr        xpr;
    Oid         opno;           /* PG_OPERATOR OID of the operator */
    Oid         opfuncid;       /* PG_PROC OID of underlying function */
    Oid         opresulttype;   /* PG_TYPE OID of result value */
    bool        opretset;       /* true if operator returns set */
    Oid         opcollid;       /* OID of collation of result */
    Oid         inputcollid;    /* OID of collation that operator should use */
    List       *args;           /* arguments to the operator (1 or 2) */
    int         location;       /* token location, or -1 if unknown */
} OpExpr;

/*
 * DistinctExpr - expression node for "x IS DISTINCT FROM y"
 *
 * Except for the nodetag, this is represented identically to an OpExpr
 * referencing the "=" operator for x and y.
 * We use "=", not the more obvious "<>", because more datatypes have "="
 * than "<>".  This means the executor must invert the operator result.
 * Note that the operator function won't be called at all if either input
 * is NULL, since then the result can be determined directly.
 */
typedef OpExpr DistinctExpr;

/*
 * NullIfExpr - a NULLIF expression
 *
 * Like DistinctExpr, this is represented the same as an OpExpr referencing
 * the "=" operator for x and y.
 */
typedef OpExpr NullIfExpr;

/*
 * ScalarArrayOpExpr - expression node for "scalar op ANY/ALL (array)"
 *
 * The operator must yield boolean.  It is applied to the left operand
 * and each element of the righthand array, and the results are combined
 * with OR or AND (for ANY or ALL respectively).  The node representation
 * is almost the same as for the underlying operator, but we need a useOr
 * flag to remember whether it's ANY or ALL, and we don't have to store
 * the result type (or the collation) because it must be boolean.
 */
typedef struct ScalarArrayOpExpr
{
    Expr        xpr;
    Oid         opno;           /* PG_OPERATOR OID of the operator */
    Oid         opfuncid;       /* PG_PROC OID of underlying function */
    bool        useOr;          /* true for ANY, false for ALL */
    Oid         inputcollid;    /* OID of collation that operator should use */
    List       *args;           /* the scalar and array operands */
    int         location;       /* token location, or -1 if unknown */
} ScalarArrayOpExpr;

/*
 * BoolExpr - expression node for the basic Boolean operators AND, OR, NOT
 *
 * Notice the arguments are given as a List.  For NOT, of course the list
 * must always have exactly one element.  For AND and OR, there can be two
 * or more arguments.
 */
typedef enum BoolExprType
{
    AND_EXPR, OR_EXPR, NOT_EXPR
} BoolExprType;

typedef struct BoolExpr
{
    Expr        xpr;
    BoolExprType boolop;
    List       *args;           /* arguments to this expression */
    int         location;       /* token location, or -1 if unknown */
} BoolExpr;

/*
 * SubLink
 *
 * A SubLink represents a subselect appearing in an expression, and in some
 * cases also the combining operator(s) just above it.  The subLinkType
 * indicates the form of the expression represented:
 *  EXISTS_SUBLINK      EXISTS(SELECT ...)
 *  ALL_SUBLINK         (lefthand) op ALL (SELECT ...)
 *  ANY_SUBLINK         (lefthand) op ANY (SELECT ...)
 *  ROWCOMPARE_SUBLINK  (lefthand) op (SELECT ...)
 *  EXPR_SUBLINK        (SELECT with single targetlist item ...)
 *  MULTIEXPR_SUBLINK   (SELECT with multiple targetlist items ...)
 *  ARRAY_SUBLINK       ARRAY(SELECT with single targetlist item ...)
 *  CTE_SUBLINK         WITH query (never actually part of an expression)
 * For ALL, ANY, and ROWCOMPARE, the lefthand is a list of expressions of the
 * same length as the subselect's targetlist.  ROWCOMPARE will *always* have
 * a list with more than one entry; if the subselect has just one target
 * then the parser will create an EXPR_SUBLINK instead (and any operator
 * above the subselect will be represented separately).
 * ROWCOMPARE, EXPR, and MULTIEXPR require the subselect to deliver at most
 * one row (if it returns no rows, the result is NULL).
 * ALL, ANY, and ROWCOMPARE require the combining operators to deliver boolean
 * results.  ALL and ANY combine the per-row results using AND and OR
 * semantics respectively.
 * ARRAY requires just one target column, and creates an array of the target
 * column's type using any number of rows resulting from the subselect.
 *
 * SubLink is classed as an Expr node, but it is not actually executable;
 * it must be replaced in the expression tree by a SubPlan node during
 * planning.
 *
 * NOTE: in the raw output of gram.y, testexpr contains just the raw form
 * of the lefthand expression (if any), and operName is the String name of
 * the combining operator.  Also, subselect is a raw parsetree.  During parse
 * analysis, the parser transforms testexpr into a complete boolean expression
 * that compares the lefthand value(s) to PARAM_SUBLINK nodes representing the
 * output columns of the subselect.  And subselect is transformed to a Query.
 * This is the representation seen in saved rules and in the rewriter.
 *
 * In EXISTS, EXPR, MULTIEXPR, and ARRAY SubLinks, testexpr and operName
 * are unused and are always null.
 *
 * subLinkId is currently used only for MULTIEXPR SubLinks, and is zero in
 * other SubLinks.  This number identifies different multiple-assignment
 * subqueries within an UPDATE statement's SET list.  It is unique only
 * within a particular targetlist.  The output column(s) of the MULTIEXPR
 * are referenced by PARAM_MULTIEXPR Params appearing elsewhere in the tlist.
 *
 * The CTE_SUBLINK case never occurs in actual SubLink nodes, but it is used
 * in SubPlans generated for WITH subqueries.
 */
typedef enum SubLinkType
{
    EXISTS_SUBLINK,
    ALL_SUBLINK,
    ANY_SUBLINK,
    ROWCOMPARE_SUBLINK,
    EXPR_SUBLINK,
    MULTIEXPR_SUBLINK,
    ARRAY_SUBLINK,
    CTE_SUBLINK                 /* for SubPlans only */
} SubLinkType;


typedef struct SubLink
{
    Expr        xpr;
    SubLinkType subLinkType;    /* see above */
    int         subLinkId;      /* ID (1..n); 0 if not MULTIEXPR */
    Node       *testexpr;       /* outer-query test for ALL/ANY/ROWCOMPARE */
    List       *operName;       /* originally specified operator name */
    Node       *subselect;      /* subselect as Query* or raw parsetree */
    int         location;       /* token location, or -1 if unknown */
} SubLink;

/*
 * SubPlan - executable expression node for a subplan (sub-SELECT)
 *
 * The planner replaces SubLink nodes in expression trees with SubPlan
 * nodes after it has finished planning the subquery.  SubPlan references
 * a sub-plantree stored in the subplans list of the toplevel PlannedStmt.
 * (We avoid a direct link to make it easier to copy expression trees
 * without causing multiple processing of the subplan.)
 *
 * In an ordinary subplan, testexpr points to an executable expression
 * (OpExpr, an AND/OR tree of OpExprs, or RowCompareExpr) for the combining
 * operator(s); the left-hand arguments are the original lefthand expressions,
 * and the right-hand arguments are PARAM_EXEC Param nodes representing the
 * outputs of the sub-select.  (NOTE: runtime coercion functions may be
 * inserted as well.)  This is just the same expression tree as testexpr in
 * the original SubLink node, but the PARAM_SUBLINK nodes are replaced by
 * suitably numbered PARAM_EXEC nodes.
 *
 * If the sub-select becomes an initplan rather than a subplan, the executable
 * expression is part of the outer plan's expression tree (and the SubPlan
 * node itself is not, but rather is found in the outer plan's initPlan
 * list).  In this case testexpr is NULL to avoid duplication.
 *
 * The planner also derives lists of the values that need to be passed into
 * and out of the subplan.  Input values are represented as a list "args" of
 * expressions to be evaluated in the outer-query context (currently these
 * args are always just Vars, but in principle they could be any expression).
 * The values are assigned to the global PARAM_EXEC params indexed by parParam
 * (the parParam and args lists must have the same ordering).  setParam is a
 * list of the PARAM_EXEC params that are computed by the sub-select, if it
 * is an initplan; they are listed in order by sub-select output column
 * position.  (parParam and setParam are integer Lists, not Bitmapsets,
 * because their ordering is significant.)
 *
 * Also, the planner computes startup and per-call costs for use of the
 * SubPlan.  Note that these include the cost of the subquery proper,
 * evaluation of the testexpr if any, and any hashtable management overhead.
 */
typedef struct SubPlan
{
    Expr        xpr;
    /* Fields copied from original SubLink: */
    SubLinkType subLinkType;    /* see above */
    /* The combining operators, transformed to an executable expression: */
    Node       *testexpr;       /* OpExpr or RowCompareExpr expression tree */
    List       *paramIds;       /* IDs of Params embedded in the above */
    /* Identification of the Plan tree to use: */
    int         plan_id;        /* Index (from 1) in PlannedStmt.subplans */
    /* Identification of the SubPlan for EXPLAIN and debugging purposes: */
    char       *plan_name;      /* A name assigned during planning */
    /* Extra data useful for determining subplan's output type: */
    Oid         firstColType;   /* Type of first column of subplan result */
    int32       firstColTypmod; /* Typmod of first column of subplan result */
    Oid         firstColCollation;  /* Collation of first column of subplan
                                     * result */
    /* Information about execution strategy: */
    bool        useHashTable;   /* true to store subselect output in a hash
                                 * table (implies we are doing "IN") */
    bool        unknownEqFalse; /* true if it's okay to return FALSE when the
                                 * spec result is UNKNOWN; this allows much
                                 * simpler handling of null values */
    bool        parallel_safe;  /* is the subplan parallel-safe? */
    /* Note: parallel_safe does not consider contents of testexpr or args */
    /* Information for passing params into and out of the subselect: */
    /* setParam and parParam are lists of integers (param IDs) */
    List       *setParam;       /* initplan subqueries have to set these
                                 * Params for parent plan */
    List       *parParam;       /* indices of input Params from parent plan */
    List       *args;           /* exprs to pass as parParam values */
    /* Estimated execution costs: */
    Cost        startup_cost;   /* one-time setup cost */
    Cost        per_call_cost;  /* cost for each subplan evaluation */
} SubPlan;

/*
 * AlternativeSubPlan - expression node for a choice among SubPlans
 *
 * This is used only transiently during planning: by the time the plan
 * reaches the executor, all AlternativeSubPlan nodes have been removed.
 *
 * The subplans are given as a List so that the node definition need not
 * change if there's ever more than two alternatives.  For the moment,
 * though, there are always exactly two; and the first one is the fast-start
 * plan.
 */
typedef struct AlternativeSubPlan
{
    Expr        xpr;
    List       *subplans;       /* SubPlan(s) with equivalent results */
} AlternativeSubPlan;

/* ----------------
 * FieldSelect
 *
 * FieldSelect represents the operation of extracting one field from a tuple
 * value.  At runtime, the input expression is expected to yield a rowtype
 * Datum.  The specified field number is extracted and returned as a Datum.
 * ----------------
 */

typedef struct FieldSelect
{
    Expr        xpr;
    Expr       *arg;            /* input expression */
    AttrNumber  fieldnum;       /* attribute number of field to extract */
    Oid         resulttype;     /* type of the field (result type of this
                                 * node) */
    int32       resulttypmod;   /* output typmod (usually -1) */
    Oid         resultcollid;   /* OID of collation of the field */
} FieldSelect;

/* ----------------
 * FieldStore
 *
 * FieldStore represents the operation of modifying one field in a tuple
 * value, yielding a new tuple value (the input is not touched!).  Like
 * the assign case of SubscriptingRef, this is used to implement UPDATE of a
 * portion of a column.
 *
 * resulttype is always a named composite type (not a domain).  To update
 * a composite domain value, apply CoerceToDomain to the FieldStore.
 *
 * A single FieldStore can actually represent updates of several different
 * fields.  The parser only generates FieldStores with single-element lists,
 * but the planner will collapse multiple updates of the same base column
 * into one FieldStore.
 * ----------------
 */

typedef struct FieldStore
{
    Expr        xpr;
    Expr       *arg;            /* input tuple value */
    List       *newvals;        /* new value(s) for field(s) */
    List       *fieldnums;      /* integer list of field attnums */
    Oid         resulttype;     /* type of result (same as type of arg) */
    /* Like RowExpr, we deliberately omit a typmod and collation here */
} FieldStore;

/* ----------------
 * RelabelType
 *
 * RelabelType represents a "dummy" type coercion between two binary-
 * compatible datatypes, such as reinterpreting the result of an OID
 * expression as an int4.  It is a no-op at runtime; we only need it
 * to provide a place to store the correct type to be attributed to
 * the expression result during type resolution.  (We can't get away
 * with just overwriting the type field of the input expression node,
 * so we need a separate node to show the coercion's result type.)
 * ----------------
 */

typedef struct RelabelType
{
    Expr        xpr;
    Expr       *arg;            /* input expression */
    Oid         resulttype;     /* output type of coercion expression */
    int32       resulttypmod;   /* output typmod (usually -1) */
    Oid         resultcollid;   /* OID of collation, or InvalidOid if none */
    CoercionForm relabelformat; /* how to display this node */
    int         location;       /* token location, or -1 if unknown */
} RelabelType;

/* ----------------
 * CoerceViaIO
 *
 * CoerceViaIO represents a type coercion between two types whose textual
 * representations are compatible, implemented by invoking the source type's
 * typoutput function then the destination type's typinput function.
 * ----------------
 */

typedef struct CoerceViaIO
{
    Expr        xpr;
    Expr       *arg;            /* input expression */
    Oid         resulttype;     /* output type of coercion */
    /* output typmod is not stored, but is presumed -1 */
    Oid         resultcollid;   /* OID of collation, or InvalidOid if none */
    CoercionForm coerceformat;  /* how to display this node */
    int         location;       /* token location, or -1 if unknown */
} CoerceViaIO;

/* ----------------
 * ArrayCoerceExpr
 *
 * ArrayCoerceExpr represents a type coercion from one array type to another,
 * which is implemented by applying the per-element coercion expression
 * "elemexpr" to each element of the source array.  Within elemexpr, the
 * source element is represented by a CaseTestExpr node.  Note that even if
 * elemexpr is a no-op (that is, just CaseTestExpr + RelabelType), the
 * coercion still requires some effort: we have to fix the element type OID
 * stored in the array header.
 * ----------------
 */

typedef struct ArrayCoerceExpr
{
    Expr        xpr;
    Expr       *arg;            /* input expression (yields an array) */
    Expr       *elemexpr;       /* expression representing per-element work */
    Oid         resulttype;     /* output type of coercion (an array type) */
    int32       resulttypmod;   /* output typmod (also element typmod) */
    Oid         resultcollid;   /* OID of collation, or InvalidOid if none */
    CoercionForm coerceformat;  /* how to display this node */
    int         location;       /* token location, or -1 if unknown */
} ArrayCoerceExpr;

/* ----------------
 * ConvertRowtypeExpr
 *
 * ConvertRowtypeExpr represents a type coercion from one composite type
 * to another, where the source type is guaranteed to contain all the columns
 * needed for the destination type plus possibly others; the columns need not
 * be in the same positions, but are matched up by name.  This is primarily
 * used to convert a whole-row value of an inheritance child table into a
 * valid whole-row value of its parent table's rowtype.  Both resulttype
 * and the exposed type of "arg" must be named composite types (not domains).
 * ----------------
 */

typedef struct ConvertRowtypeExpr
{
    Expr        xpr;
    Expr       *arg;            /* input expression */
    Oid         resulttype;     /* output type (always a composite type) */
    /* Like RowExpr, we deliberately omit a typmod and collation here */
    CoercionForm convertformat; /* how to display this node */
    int         location;       /* token location, or -1 if unknown */
} ConvertRowtypeExpr;

/*----------
 * CollateExpr - COLLATE
 *
 * The planner replaces CollateExpr with RelabelType during expression
 * preprocessing, so execution never sees a CollateExpr.
 *----------
 */
typedef struct CollateExpr
{
    Expr        xpr;
    Expr       *arg;            /* input expression */
    Oid         collOid;        /* collation's OID */
    int         location;       /* token location, or -1 if unknown */
} CollateExpr;

/*----------
 * CaseExpr - a CASE expression
 *
 * We support two distinct forms of CASE expression:
 *      CASE WHEN boolexpr THEN expr [ WHEN boolexpr THEN expr ... ]
 *      CASE testexpr WHEN compexpr THEN expr [ WHEN compexpr THEN expr ... ]
 * These are distinguishable by the "arg" field being NULL in the first case
 * and the testexpr in the second case.
 *
 * In the raw grammar output for the second form, the condition expressions
 * of the WHEN clauses are just the comparison values.  Parse analysis
 * converts these to valid boolean expressions of the form
 *      CaseTestExpr '=' compexpr
 * where the CaseTestExpr node is a placeholder that emits the correct
 * value at runtime.  This structure is used so that the testexpr need be
 * evaluated only once.  Note that after parse analysis, the condition
 * expressions always yield boolean.
 *
 * Note: we can test whether a CaseExpr has been through parse analysis
 * yet by checking whether casetype is InvalidOid or not.
 *----------
 */
typedef struct CaseExpr
{
    Expr        xpr;
    Oid         casetype;       /* type of expression result */
    Oid         casecollid;     /* OID of collation, or InvalidOid if none */
    Expr       *arg;            /* implicit equality comparison argument */
    List       *args;           /* the arguments (list of WHEN clauses) */
    Expr       *defresult;      /* the default result (ELSE clause) */
    int         location;       /* token location, or -1 if unknown */
} CaseExpr;

/*
 * CaseWhen - one arm of a CASE expression
 */
typedef struct CaseWhen
{
    Expr        xpr;
    Expr       *expr;           /* condition expression */
    Expr       *result;         /* substitution result */
    int         location;       /* token location, or -1 if unknown */
} CaseWhen;

/*
 * Placeholder node for the test value to be processed by a CASE expression.
 * This is effectively like a Param, but can be implemented more simply
 * since we need only one replacement value at a time.
 *
 * We also abuse this node type for some other purposes, including:
 *  * Placeholder for the current array element value in ArrayCoerceExpr;
 *    see build_coercion_expression().
 *  * Nested FieldStore/SubscriptingRef assignment expressions in INSERT/UPDATE;
 *    see transformAssignmentIndirection().
 *
 * The uses in CaseExpr and ArrayCoerceExpr are safe only to the extent that
 * there is not any other CaseExpr or ArrayCoerceExpr between the value source
 * node and its child CaseTestExpr(s).  This is true in the parse analysis
 * output, but the planner's function-inlining logic has to be careful not to
 * break it.
 *
 * The nested-assignment-expression case is safe because the only node types
 * that can be above such CaseTestExprs are FieldStore and SubscriptingRef.
 */
typedef struct CaseTestExpr
{
    Expr        xpr;
    Oid         typeId;         /* type for substituted value */
    int32       typeMod;        /* typemod for substituted value */
    Oid         collation;      /* collation for the substituted value */
} CaseTestExpr;

/*
 * ArrayExpr - an ARRAY[] expression
 *
 * Note: if multidims is false, the constituent expressions all yield the
 * scalar type identified by element_typeid.  If multidims is true, the
 * constituent expressions all yield arrays of element_typeid (ie, the same
 * type as array_typeid); at runtime we must check for compatible subscripts.
 */
typedef struct ArrayExpr
{
    Expr        xpr;
    Oid         array_typeid;   /* type of expression result */
    Oid         array_collid;   /* OID of collation, or InvalidOid if none */
    Oid         element_typeid; /* common type of array elements */
    List       *elements;       /* the array elements or sub-arrays */
    bool        multidims;      /* true if elements are sub-arrays */
    int         location;       /* token location, or -1 if unknown */
} ArrayExpr;

/*
 * RowExpr - a ROW() expression
 *
 * Note: the list of fields must have a one-for-one correspondence with
 * physical fields of the associated rowtype, although it is okay for it
 * to be shorter than the rowtype.  That is, the N'th list element must
 * match up with the N'th physical field.  When the N'th physical field
 * is a dropped column (attisdropped) then the N'th list element can just
 * be a NULL constant.  (This case can only occur for named composite types,
 * not RECORD types, since those are built from the RowExpr itself rather
 * than vice versa.)  It is important not to assume that length(args) is
 * the same as the number of columns logically present in the rowtype.
 *
 * colnames provides field names in cases where the names can't easily be
 * obtained otherwise.  Names *must* be provided if row_typeid is RECORDOID.
 * If row_typeid identifies a known composite type, colnames can be NIL to
 * indicate the type's cataloged field names apply.  Note that colnames can
 * be non-NIL even for a composite type, and typically is when the RowExpr
 * was created by expanding a whole-row Var.  This is so that we can retain
 * the column alias names of the RTE that the Var referenced (which would
 * otherwise be very difficult to extract from the parsetree).  Like the
 * args list, colnames is one-for-one with physical fields of the rowtype.
 */
typedef struct RowExpr
{
    Expr        xpr;
    List       *args;           /* the fields */
    Oid         row_typeid;     /* RECORDOID or a composite type's ID */

    /*
     * row_typeid cannot be a domain over composite, only plain composite.  To
     * create a composite domain value, apply CoerceToDomain to the RowExpr.
     *
     * Note: we deliberately do NOT store a typmod.  Although a typmod will be
     * associated with specific RECORD types at runtime, it will differ for
     * different backends, and so cannot safely be stored in stored
     * parsetrees.  We must assume typmod -1 for a RowExpr node.
     *
     * We don't need to store a collation either.  The result type is
     * necessarily composite, and composite types never have a collation.
     */
    CoercionForm row_format;    /* how to display this node */
    List       *colnames;       /* list of String, or NIL */
    int         location;       /* token location, or -1 if unknown */
} RowExpr;

/*
 * RowCompareExpr - row-wise comparison, such as (a, b) <= (1, 2)
 *
 * We support row comparison for any operator that can be determined to
 * act like =, <>, <, <=, >, or >= (we determine this by looking for the
 * operator in btree opfamilies).  Note that the same operator name might
 * map to a different operator for each pair of row elements, since the
 * element datatypes can vary.
 *
 * A RowCompareExpr node is only generated for the < <= > >= cases;
 * the = and <> cases are translated to simple AND or OR combinations
 * of the pairwise comparisons.  However, we include = and <> in the
 * RowCompareType enum for the convenience of parser logic.
 */
typedef enum RowCompareType
{
    /* Values of this enum are chosen to match btree strategy numbers */
    ROWCOMPARE_LT = 1,          /* BTLessStrategyNumber */
    ROWCOMPARE_LE = 2,          /* BTLessEqualStrategyNumber */
    ROWCOMPARE_EQ = 3,          /* BTEqualStrategyNumber */
    ROWCOMPARE_GE = 4,          /* BTGreaterEqualStrategyNumber */
    ROWCOMPARE_GT = 5,          /* BTGreaterStrategyNumber */
    ROWCOMPARE_NE = 6           /* no such btree strategy */
} RowCompareType;

typedef struct RowCompareExpr
{
    Expr        xpr;
    RowCompareType rctype;      /* LT LE GE or GT, never EQ or NE */
    List       *opnos;          /* OID list of pairwise comparison ops */
    List       *opfamilies;     /* OID list of containing operator families */
    List       *inputcollids;   /* OID list of collations for comparisons */
    List       *largs;          /* the left-hand input arguments */
    List       *rargs;          /* the right-hand input arguments */
} RowCompareExpr;

/*
 * CoalesceExpr - a COALESCE expression
 */
typedef struct CoalesceExpr
{
    Expr        xpr;
    Oid         coalescetype;   /* type of expression result */
    Oid         coalescecollid; /* OID of collation, or InvalidOid if none */
    List       *args;           /* the arguments */
    int         location;       /* token location, or -1 if unknown */
} CoalesceExpr;

/*
 * MinMaxExpr - a GREATEST or LEAST function
 */
typedef enum MinMaxOp
{
    IS_GREATEST,
    IS_LEAST
} MinMaxOp;

typedef struct MinMaxExpr
{
    Expr        xpr;
    Oid         minmaxtype;     /* common type of arguments and result */
    Oid         minmaxcollid;   /* OID of collation of result */
    Oid         inputcollid;    /* OID of collation that function should use */
    MinMaxOp    op;             /* function to execute */
    List       *args;           /* the arguments */
    int         location;       /* token location, or -1 if unknown */
} MinMaxExpr;

/*
 * SQLValueFunction - parameterless functions with special grammar productions
 *
 * The SQL standard categorizes some of these as <datetime value function>
 * and others as <general value specification>.  We call 'em SQLValueFunctions
 * for lack of a better term.  We store type and typmod of the result so that
 * some code doesn't need to know each function individually, and because
 * we would need to store typmod anyway for some of the datetime functions.
 * Note that currently, all variants return non-collating datatypes, so we do
 * not need a collation field; also, all these functions are stable.
 */
typedef enum SQLValueFunctionOp
{
    SVFOP_CURRENT_DATE,
    SVFOP_CURRENT_TIME,
    SVFOP_CURRENT_TIME_N,
    SVFOP_CURRENT_TIMESTAMP,
    SVFOP_CURRENT_TIMESTAMP_N,
    SVFOP_LOCALTIME,
    SVFOP_LOCALTIME_N,
    SVFOP_LOCALTIMESTAMP,
    SVFOP_LOCALTIMESTAMP_N,
    SVFOP_CURRENT_ROLE,
    SVFOP_CURRENT_USER,
    SVFOP_USER,
    SVFOP_SESSION_USER,
    SVFOP_CURRENT_CATALOG,
    SVFOP_CURRENT_SCHEMA
} SQLValueFunctionOp;

typedef struct SQLValueFunction
{
    Expr        xpr;
    SQLValueFunctionOp op;      /* which function this is */
    Oid         type;           /* result type/typmod */
    int32       typmod;
    int         location;       /* token location, or -1 if unknown */
} SQLValueFunction;

/*
 * XmlExpr - various SQL/XML functions requiring special grammar productions
 *
 * 'name' carries the "NAME foo" argument (already XML-escaped).
 * 'named_args' and 'arg_names' represent an xml_attribute list.
 * 'args' carries all other arguments.
 *
 * Note: result type/typmod/collation are not stored, but can be deduced
 * from the XmlExprOp.  The type/typmod fields are just used for display
 * purposes, and are NOT necessarily the true result type of the node.
 */
typedef enum XmlExprOp
{
    IS_XMLCONCAT,               /* XMLCONCAT(args) */
    IS_XMLELEMENT,              /* XMLELEMENT(name, xml_attributes, args) */
    IS_XMLFOREST,               /* XMLFOREST(xml_attributes) */
    IS_XMLPARSE,                /* XMLPARSE(text, is_doc, preserve_ws) */
    IS_XMLPI,                   /* XMLPI(name [, args]) */
    IS_XMLROOT,                 /* XMLROOT(xml, version, standalone) */
    IS_XMLSERIALIZE,            /* XMLSERIALIZE(is_document, xmlval) */
    IS_DOCUMENT                 /* xmlval IS DOCUMENT */
} XmlExprOp;

typedef enum
{
    XMLOPTION_DOCUMENT,
    XMLOPTION_CONTENT
} XmlOptionType;

typedef struct XmlExpr
{
    Expr        xpr;
    XmlExprOp   op;             /* xml function ID */
    char       *name;           /* name in xml(NAME foo ...) syntaxes */
    List       *named_args;     /* non-XML expressions for xml_attributes */
    List       *arg_names;      /* parallel list of Value strings */
    List       *args;           /* list of expressions */
    XmlOptionType xmloption;    /* DOCUMENT or CONTENT */
    Oid         type;           /* target type/typmod for XMLSERIALIZE */
    int32       typmod;
    int         location;       /* token location, or -1 if unknown */
} XmlExpr;

/* ----------------
 * NullTest
 *
 * NullTest represents the operation of testing a value for NULLness.
 * The appropriate test is performed and returned as a boolean Datum.
 *
 * When argisrow is false, this simply represents a test for the null value.
 *
 * When argisrow is true, the input expression must yield a rowtype, and
 * the node implements "row IS [NOT] NULL" per the SQL standard.  This
 * includes checking individual fields for NULLness when the row datum
 * itself isn't NULL.
 *
 * NOTE: the combination of a rowtype input and argisrow==false does NOT
 * correspond to the SQL notation "row IS [NOT] NULL"; instead, this case
 * represents the SQL notation "row IS [NOT] DISTINCT FROM NULL".
 * ----------------
 */

typedef enum NullTestType
{
    IS_NULL, IS_NOT_NULL
} NullTestType;

typedef struct NullTest
{
    Expr        xpr;
    Expr       *arg;            /* input expression */
    NullTestType nulltesttype;  /* IS NULL, IS NOT NULL */
    bool        argisrow;       /* T to perform field-by-field null checks */
    int         location;       /* token location, or -1 if unknown */
} NullTest;

/*
 * BooleanTest
 *
 * BooleanTest represents the operation of determining whether a boolean
 * is TRUE, FALSE, or UNKNOWN (ie, NULL).  All six meaningful combinations
 * are supported.  Note that a NULL input does *not* cause a NULL result.
 * The appropriate test is performed and returned as a boolean Datum.
 */

typedef enum BoolTestType
{
    IS_TRUE, IS_NOT_TRUE, IS_FALSE, IS_NOT_FALSE, IS_UNKNOWN, IS_NOT_UNKNOWN
} BoolTestType;

typedef struct BooleanTest
{
    Expr        xpr;
    Expr       *arg;            /* input expression */
    BoolTestType booltesttype;  /* test type */
    int         location;       /* token location, or -1 if unknown */
} BooleanTest;

/*
 * CoerceToDomain
 *
 * CoerceToDomain represents the operation of coercing a value to a domain
 * type.  At runtime (and not before) the precise set of constraints to be
 * checked will be determined.  If the value passes, it is returned as the
 * result; if not, an error is raised.  Note that this is equivalent to
 * RelabelType in the scenario where no constraints are applied.
 */
typedef struct CoerceToDomain
{
    Expr        xpr;
    Expr       *arg;            /* input expression */
    Oid         resulttype;     /* domain type ID (result type) */
    int32       resulttypmod;   /* output typmod (currently always -1) */
    Oid         resultcollid;   /* OID of collation, or InvalidOid if none */
    CoercionForm coercionformat;    /* how to display this node */
    int         location;       /* token location, or -1 if unknown */
} CoerceToDomain;

/*
 * Placeholder node for the value to be processed by a domain's check
 * constraint.  This is effectively like a Param, but can be implemented more
 * simply since we need only one replacement value at a time.
 *
 * Note: the typeId/typeMod/collation will be set from the domain's base type,
 * not the domain itself.  This is because we shouldn't consider the value
 * to be a member of the domain if we haven't yet checked its constraints.
 */
typedef struct CoerceToDomainValue
{
    Expr        xpr;
    Oid         typeId;         /* type for substituted value */
    int32       typeMod;        /* typemod for substituted value */
    Oid         collation;      /* collation for the substituted value */
    int         location;       /* token location, or -1 if unknown */
} CoerceToDomainValue;

/*
 * Placeholder node for a DEFAULT marker in an INSERT or UPDATE command.
 *
 * This is not an executable expression: it must be replaced by the actual
 * column default expression during rewriting.  But it is convenient to
 * treat it as an expression node during parsing and rewriting.
 */
typedef struct SetToDefault
{
    Expr        xpr;
    Oid         typeId;         /* type for substituted value */
    int32       typeMod;        /* typemod for substituted value */
    Oid         collation;      /* collation for the substituted value */
    int         location;       /* token location, or -1 if unknown */
} SetToDefault;

/*
 * Node representing [WHERE] CURRENT OF cursor_name
 *
 * CURRENT OF is a bit like a Var, in that it carries the rangetable index
 * of the target relation being constrained; this aids placing the expression
 * correctly during planning.  We can assume however that its "levelsup" is
 * always zero, due to the syntactic constraints on where it can appear.
 *
 * The referenced cursor can be represented either as a hardwired string
 * or as a reference to a run-time parameter of type REFCURSOR.  The latter
 * case is for the convenience of plpgsql.
 */
typedef struct CurrentOfExpr
{
    Expr        xpr;
    Index       cvarno;         /* RT index of target relation */
    char       *cursor_name;    /* name of referenced cursor, or NULL */
    int         cursor_param;   /* refcursor parameter number, or 0 */
} CurrentOfExpr;

/*
 * NextValueExpr - get next value from sequence
 *
 * This has the same effect as calling the nextval() function, but it does not
 * check permissions on the sequence.  This is used for identity columns,
 * where the sequence is an implicit dependency without its own permissions.
 */
typedef struct NextValueExpr
{
    Expr        xpr;
    Oid         seqid;
    Oid         typeId;
} NextValueExpr;

/*
 * InferenceElem - an element of a unique index inference specification
 *
 * This mostly matches the structure of IndexElems, but having a dedicated
 * primnode allows for a clean separation between the use of index parameters
 * by utility commands, and this node.
 */
typedef struct InferenceElem
{
    Expr        xpr;
    Node       *expr;           /* expression to infer from, or NULL */
    Oid         infercollid;    /* OID of collation, or InvalidOid */
    Oid         inferopclass;   /* OID of att opclass, or InvalidOid */
} InferenceElem;

/*--------------------
 * TargetEntry -
 *     a target entry (used in query target lists)
 *
 * Strictly speaking, a TargetEntry isn't an expression node (since it can't
 * be evaluated by ExecEvalExpr).  But we treat it as one anyway, since in
 * very many places it's convenient to process a whole query targetlist as a
 * single expression tree.
 *
 * In a SELECT's targetlist, resno should always be equal to the item's
 * ordinal position (counting from 1).  However, in an INSERT or UPDATE
 * targetlist, resno represents the attribute number of the destination
 * column for the item; so there may be missing or out-of-order resnos.
 * It is even legal to have duplicated resnos; consider
 *      UPDATE table SET arraycol[1] = ..., arraycol[2] = ..., ...
 * The two meanings come together in the executor, because the planner
 * transforms INSERT/UPDATE tlists into a normalized form with exactly
 * one entry for each column of the destination table.  Before that's
 * happened, however, it is risky to assume that resno == position.
 * Generally get_tle_by_resno() should be used rather than list_nth()
 * to fetch tlist entries by resno, and only in SELECT should you assume
 * that resno is a unique identifier.
 *
 * resname is required to represent the correct column name in non-resjunk
 * entries of top-level SELECT targetlists, since it will be used as the
 * column title sent to the frontend.  In most other contexts it is only
 * a debugging aid, and may be wrong or even NULL.  (In particular, it may
 * be wrong in a tlist from a stored rule, if the referenced column has been
 * renamed by ALTER TABLE since the rule was made.  Also, the planner tends
 * to store NULL rather than look up a valid name for tlist entries in
 * non-toplevel plan nodes.)  In resjunk entries, resname should be either
 * a specific system-generated name (such as "ctid") or NULL; anything else
 * risks confusing ExecGetJunkAttribute!
 *
 * ressortgroupref is used in the representation of ORDER BY, GROUP BY, and
 * DISTINCT items.  Targetlist entries with ressortgroupref=0 are not
 * sort/group items.  If ressortgroupref>0, then this item is an ORDER BY,
 * GROUP BY, and/or DISTINCT target value.  No two entries in a targetlist
 * may have the same nonzero ressortgroupref --- but there is no particular
 * meaning to the nonzero values, except as tags.  (For example, one must
 * not assume that lower ressortgroupref means a more significant sort key.)
 * The order of the associated SortGroupClause lists determine the semantics.
 *
 * resorigtbl/resorigcol identify the source of the column, if it is a
 * simple reference to a column of a base table (or view).  If it is not
 * a simple reference, these fields are zeroes.
 *
 * If resjunk is true then the column is a working column (such as a sort key)
 * that should be removed from the final output of the query.  Resjunk columns
 * must have resnos that cannot duplicate any regular column's resno.  Also
 * note that there are places that assume resjunk columns come after non-junk
 * columns.
 *--------------------
 */
typedef struct TargetEntry
{
    Expr        xpr;
    Expr       *expr;           /* expression to evaluate */
    AttrNumber  resno;          /* attribute number (see notes above) */
    char       *resname;        /* name of the column (could be NULL) */
    Index       ressortgroupref;    /* nonzero if referenced by a sort/group
                                     * clause */
    Oid         resorigtbl;     /* OID of column's source table */
    AttrNumber  resorigcol;     /* column's number in source table */
    bool        resjunk;        /* set to true to eliminate the attribute from
                                 * final target list */
} TargetEntry;


/* ----------------------------------------------------------------
 *                  node types for join trees
 *
 * The leaves of a join tree structure are RangeTblRef nodes.  Above
 * these, JoinExpr nodes can appear to denote a specific kind of join
 * or qualified join.  Also, FromExpr nodes can appear to denote an
 * ordinary cross-product join ("FROM foo, bar, baz WHERE ...").
 * FromExpr is like a JoinExpr of jointype JOIN_INNER, except that it
 * may have any number of child nodes, not just two.
 *
 * NOTE: the top level of a Query's jointree is always a FromExpr.
 * Even if the jointree contains no rels, there will be a FromExpr.
 *
 * NOTE: the qualification expressions present in JoinExpr nodes are
 * *in addition to* the query's main WHERE clause, which appears as the
 * qual of the top-level FromExpr.  The reason for associating quals with
 * specific nodes in the jointree is that the position of a qual is critical
 * when outer joins are present.  (If we enforce a qual too soon or too late,
 * that may cause the outer join to produce the wrong set of NULL-extended
 * rows.)  If all joins are inner joins then all the qual positions are
 * semantically interchangeable.
 *
 * NOTE: in the raw output of gram.y, a join tree contains RangeVar,
 * RangeSubselect, and RangeFunction nodes, which are all replaced by
 * RangeTblRef nodes during the parse analysis phase.  Also, the top-level
 * FromExpr is added during parse analysis; the grammar regards FROM and
 * WHERE as separate.
 * ----------------------------------------------------------------
 */

/*
 * RangeTblRef - reference to an entry in the query's rangetable
 *
 * We could use direct pointers to the RT entries and skip having these
 * nodes, but multiple pointers to the same node in a querytree cause
 * lots of headaches, so it seems better to store an index into the RT.
 */
typedef struct RangeTblRef
{
    NodeTag     type;
    int         rtindex;
} RangeTblRef;

/*----------
 * JoinExpr - for SQL JOIN expressions
 *
 * isNatural, usingClause, and quals are interdependent.  The user can write
 * only one of NATURAL, USING(), or ON() (this is enforced by the grammar).
 * If he writes NATURAL then parse analysis generates the equivalent USING()
 * list, and from that fills in "quals" with the right equality comparisons.
 * If he writes USING() then "quals" is filled with equality comparisons.
 * If he writes ON() then only "quals" is set.  Note that NATURAL/USING
 * are not equivalent to ON() since they also affect the output column list.
 *
 * alias is an Alias node representing the AS alias-clause attached to the
 * join expression, or NULL if no clause.  NB: presence or absence of the
 * alias has a critical impact on semantics, because a join with an alias
 * restricts visibility of the tables/columns inside it.
 *
 * During parse analysis, an RTE is created for the Join, and its index
 * is filled into rtindex.  This RTE is present mainly so that Vars can
 * be created that refer to the outputs of the join.  The planner sometimes
 * generates JoinExprs internally; these can have rtindex = 0 if there are
 * no join alias variables referencing such joins.
 *----------
 */
typedef struct JoinExpr
{
    NodeTag     type;
    JoinType    jointype;       /* type of join */
    bool        isNatural;      /* Natural join? Will need to shape table */
    Node       *larg;           /* left subtree */
    Node       *rarg;           /* right subtree */
    List       *usingClause;    /* USING clause, if any (list of String) */
    Node       *quals;          /* qualifiers on join, if any */
    Alias      *alias;          /* user-written alias clause, if any */
    int         rtindex;        /* RT index assigned for join, or 0 */
} JoinExpr;

/*----------
 * FromExpr - represents a FROM ... WHERE ... construct
 *
 * This is both more flexible than a JoinExpr (it can have any number of
 * children, including zero) and less so --- we don't need to deal with
 * aliases and so on.  The output column set is implicitly just the union
 * of the outputs of the children.
 *----------
 */
typedef struct FromExpr
{
    NodeTag     type;
    List       *fromlist;       /* List of join subtrees */
    Node       *quals;          /* qualifiers on join, if any */
} FromExpr;

/*----------
 * OnConflictExpr - represents an ON CONFLICT DO ... expression
 *
 * The optimizer requires a list of inference elements, and optionally a WHERE
 * clause to infer a unique index.  The unique index (or, occasionally,
 * indexes) inferred are used to arbitrate whether or not the alternative ON
 * CONFLICT path is taken.
 *----------
 */
typedef struct OnConflictExpr
{
    NodeTag     type;
    OnConflictAction action;    /* DO NOTHING or UPDATE? */

    /* Arbiter */
    List       *arbiterElems;   /* unique index arbiter list (of
                                 * InferenceElem's) */
    Node       *arbiterWhere;   /* unique index arbiter WHERE clause */
    Oid         constraint;     /* pg_constraint OID for arbiter */

    /* ON CONFLICT UPDATE */
    List       *onConflictSet;  /* List of ON CONFLICT SET TargetEntrys */
    Node       *onConflictWhere;    /* qualifiers to restrict UPDATE to */
    int         exclRelIndex;   /* RT index of 'excluded' relation */
    List       *exclRelTlist;   /* tlist of the EXCLUDED pseudo relation */
} OnConflictExpr;

#endif                          /* PRIMNODES_H */