/*-------------------------------------------------------------------------
 *
 * 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) 1996-2017, PostgreSQL Global Development PGGroup
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/nodes/primnodes.h
 *
 *-------------------------------------------------------------------------
 */
#pragma once

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

namespace duckdb_libpgquery {

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

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

/* What to do at commit time for temporary relations */
typedef enum PGOnCommitAction {
	PG_ONCOMMIT_NOOP,          /* No ON COMMIT clause (do nothing) */
	PG_ONCOMMIT_PRESERVE_ROWS, /* ON COMMIT PRESERVE ROWS (do nothing) */
	PG_ONCOMMIT_DELETE_ROWS,   /* ON COMMIT DELETE ROWS */
	ONCOMMIT_DROP              /* ON COMMIT DROP */
} PGOnCommitAction;

/* What to do at commit time for temporary relations */
typedef enum PGOnCreateConflict {
	// Standard: throw error
	PG_ERROR_ON_CONFLICT,
	// CREATE IF NOT EXISTS, silently do nothing on conflict
	PG_IGNORE_ON_CONFLICT,
	// CREATE OR REPLACE
	PG_REPLACE_ON_CONFLICT
} PGOnCreateConflict;

/*
 * PGRangeVar - 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 PGRangeVar {
	PGNodeTag 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 */
	PGAlias *alias;      /* table alias & optional column aliases */
	int location;        /* token location, or -1 if unknown */
	PGNode *sample;      /* sample, if any */
} PGRangeVar;

/*
 * PGTableFunc - node for a table function, such as XMLTABLE.
 */
typedef struct PGTableFunc {
	PGNodeTag type;
	PGList *ns_uris;       /* list of namespace uri */
	PGList *ns_names;      /* list of namespace names */
	PGNode *docexpr;       /* input document expression */
	PGNode *rowexpr;       /* row filter expression */
	PGList *colnames;      /* column names (list of String) */
	PGList *coltypes;      /* OID list of column type OIDs */
	PGList *coltypmods;    /* integer list of column typmods */
	PGList *colcollations; /* OID list of column collation OIDs */
	PGList *colexprs;      /* list of column filter expressions */
	PGList *coldefexprs;   /* list of column default expressions */
	PGBitmapset *notnulls; /* nullability flag for each output column */
	int ordinalitycol;     /* counts from 0; -1 if none specified */
	int location;          /* token location, or -1 if unknown */
} PGTableFunc;

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

	PGRangeVar *rel;           /* target relation name */
	PGList *colNames;          /* column names to assign, or NIL */
	PGList *options;           /* options from WITH clause */
	PGOnCommitAction onCommit; /* what do we do at COMMIT? */
	char *tableSpaceName;      /* table space to use, or NULL */
	PGNode *viewQuery;         /* materialized view's SELECT query */
	bool skipData;             /* true for WITH NO DATA */
} PGIntoClause;

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

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

/*
 * PGVar - expression node representing a variable (ie, a table column)
 *
 * Note: during parsing/planning, varnoold/varoattno are always just copies
 * of varno/varattno.  At the tail end of planning, PGVar 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 PGForeignScan and PGCustomScan
 * plan nodes, INDEX_VAR is abused to signify references to columns of a
 * custom scan tuple type.)  In all these cases, varnoold/varoattno hold the
 * original values.  The code doesn't really need varnoold/varoattno, but they
 * are very useful for debugging and interpreting completed plans, so we keep
 * them around.
 */
#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 PGVar {
	PGExpr xpr;
	PGIndex varno;          /* index of this var's relation in the range
								 * table, or INNER_VAR/OUTER_VAR/INDEX_VAR */
	PGAttrNumber varattno;  /* attribute number of this var, or zero for
								 * all */
	PGOid vartype;          /* pg_type OID for the type of this var */
	int32_t vartypmod;      /* pg_attribute typmod value */
	PGOid varcollid;        /* OID of collation, or InvalidOid if none */
	PGIndex varlevelsup;    /* for subquery variables referencing outer
								 * relations; 0 in a normal var, >0 means N
								 * levels up */
	PGIndex varnoold;       /* original value of varno, for debugging */
	PGAttrNumber varoattno; /* original value of varattno */
	int location;           /* token location, or -1 if unknown */
} PGVar;

/*
 * PGConst
 *
 * Note: for pg_varlena data types, we make a rule that a PGConst node's value
 * must be in non-extended form (4-byte header, no compression or external
 * references).  This ensures that the PGConst node is self-contained and makes
 * it more likely that equal() will see logically identical values as equal.
 */
typedef struct PGConst {
	PGExpr xpr;
	PGOid consttype;     /* pg_type OID of the constant's datatype */
	int32_t consttypmod; /* typmod value, if any */
	PGOid constcollid;   /* OID of collation, or InvalidOid if none */
	int constlen;        /* typlen of the constant's datatype */
	PGDatum 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 PGDatum
								 * contains a pointer to the information. */
	int location;        /* token location, or -1 if unknown */
} PGConst;

/*
 * PGParam
 *
 *		paramkind specifies the kind of parameter. The possible values
 *		for this field are:
 *
 *		PG_PARAM_EXTERN:  The parameter value is supplied from outside the plan.
 *				Such parameters are numbered from 1 to n.
 *
 *		PG_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 PG_PARAM_EXTERN numbers.
 *
 *		PG_PARAM_SUBLINK:	The parameter represents an output column of a PGSubLink
 *				node's sub-select.  The column number is contained in the
 *				`paramid' field.  (This type of PGParam is converted to
 *				PG_PARAM_EXEC during planning.)
 *
 *		PG_PARAM_MULTIEXPR:  Like PG_PARAM_SUBLINK, the parameter represents an
 *				output column of a PGSubLink node's sub-select, but here, the
 *				PGSubLink 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 PGParam is also converted to PG_PARAM_EXEC during planning.)
 */
typedef enum PGParamKind { PG_PARAM_EXTERN, PG_PARAM_EXEC, PG_PARAM_SUBLINK, PG_PARAM_MULTIEXPR } PGParamKind;

typedef struct PGParam {
	PGExpr xpr;
	PGParamKind paramkind; /* kind of parameter. See above */
	int paramid;           /* numeric ID for parameter */
	PGOid paramtype;       /* pg_type OID of parameter's datatype */
	int32_t paramtypmod;   /* typmod value, if known */
	PGOid paramcollid;     /* OID of collation, or InvalidOid if none */
	int location;          /* token location, or -1 if unknown */
} PGParam;

/*
 * PGAggref
 *
 * The aggregate's args list is a targetlist, ie, a list of PGTargetEntry 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 PGQuery, the TLEs can be marked with
 * ressortgroupref indexes to let them be referenced by PGSortGroupClause
 * 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 PGTargetEntry 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 PG_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.
 */
typedef struct PGAggref {
	PGExpr xpr;
	PGOid aggfnoid;        /* pg_proc PGOid of the aggregate */
	PGOid aggtype;         /* type PGOid of result of the aggregate */
	PGOid aggcollid;       /* OID of collation of result */
	PGOid inputcollid;     /* OID of collation that function should use */
	PGOid aggtranstype;    /* type PGOid of aggregate's transition value */
	PGList *aggargtypes;   /* type Oids of direct and aggregated args */
	PGList *aggdirectargs; /* direct arguments, if an ordered-set agg */
	PGList *args;          /* aggregated arguments and sort expressions */
	PGList *aggorder;      /* ORDER BY (list of PGSortGroupClause) */
	PGList *aggdistinct;   /* DISTINCT (list of PGSortGroupClause) */
	PGExpr *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) */
	PGIndex agglevelsup;   /* > 0 if agg belongs to outer query */
	PGAggSplit aggsplit;   /* expected agg-splitting mode of parent PGAgg */
	int location;          /* token location, or -1 if unknown */
} PGAggref;

/*
 * PGGroupingFunc
 *
 * A PGGroupingFunc 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 PGAgg 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 PGGroupingFunc 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 PGGroupingFunc {
	PGExpr xpr;
	PGList *args;        /* arguments, not evaluated but kept for
								 * benefit of EXPLAIN etc. */
	PGList *refs;        /* ressortgrouprefs of arguments */
	PGList *cols;        /* actual column positions set by planner */
	PGIndex agglevelsup; /* same as Aggref.agglevelsup */
	int location;        /* token location */
} PGGroupingFunc;

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

/* ----------------
 *	PGArrayRef: describes an array subscripting operation
 *
 * An PGArrayRef can describe fetching a single element from an array,
 * fetching a subarray (array slice), storing a single element into
 * an array, or storing a slice.  The "store" cases work with an
 * initial array value and a source value that is inserted into the
 * appropriate part of the array; the result of the operation is an
 * entire new modified array value.
 *
 * If reflowerindexpr = NIL, then we are fetching or storing a single array
 * element at the subscripts given by refupperindexpr.  Otherwise we are
 * fetching or storing an array slice, that is a rectangular subarray
 * 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".
 *
 * Note: the result datatype is the element type when fetching a single
 * element; but it is the array type when doing subarray fetch or either
 * type of store.
 *
 * Note: for the cases where an array is returned, if refexpr yields a R/W
 * expanded array, then the implementation is allowed to modify that object
 * in-place and return the same object.)
 * ----------------
 */
typedef struct PGArrayRef {
	PGExpr xpr;
	PGOid refarraytype;      /* type of the array proper */
	PGOid refelemtype;       /* type of the array elements */
	int32_t reftypmod;       /* typmod of the array (and elements too) */
	PGOid refcollid;         /* OID of collation, or InvalidOid if none */
	PGList *refupperindexpr; /* expressions that evaluate to upper
									 * array indexes */
	PGList *reflowerindexpr; /* expressions that evaluate to lower
									 * array indexes, or NIL for single array
									 * element */
	PGExpr *refexpr;         /* the expression that evaluates to an array
								 * value */
	PGExpr *refassgnexpr;    /* expression for the source value, or NULL if
								 * fetch */
} PGArrayRef;

/*
 * PGCoercionContext - 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 PGCoercionContext {
	PG_COERCION_IMPLICIT,   /* coercion in context of expression */
	PG_COERCION_ASSIGNMENT, /* coercion in context of assignment */
	PG_COERCION_EXPLICIT    /* explicit cast operation */
} PGCoercionContext;

/*
 * PGCoercionForm - how to display a node that could have come from a cast
 *
 * NB: equal() ignores PGCoercionForm 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 PGCoercionForm {
	PG_COERCE_EXPLICIT_CALL, /* display as a function call */
	PG_COERCE_EXPLICIT_CAST, /* display as an explicit cast */
	PG_COERCE_IMPLICIT_CAST  /* implicit cast, so hide it */
} PGCoercionForm;

/*
 * PGFuncExpr - expression node for a function call
 */
typedef struct PGFuncExpr {
	PGExpr xpr;
	PGOid funcid;              /* PG_PROC OID of the function */
	PGOid 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 */
	PGCoercionForm funcformat; /* how to display this function call */
	PGOid funccollid;          /* OID of collation of result */
	PGOid inputcollid;         /* OID of collation that function should use */
	PGList *args;              /* arguments to the function */
	int location;              /* token location, or -1 if unknown */
} PGFuncExpr;

/*
 * PGNamedArgExpr - a named argument of a function
 *
 * This node type can only appear in the args list of a PGFuncCall or PGFuncExpr
 * 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 PGNamedArgExpr {
	PGExpr xpr;
	PGExpr *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 */
} PGNamedArgExpr;

/*
 * PGOpExpr - 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 PGOpExpr {
	PGExpr xpr;
	PGOid opno;         /* PG_OPERATOR OID of the operator */
	PGOid opfuncid;     /* PG_PROC OID of underlying function */
	PGOid opresulttype; /* PG_TYPE OID of result value */
	bool opretset;      /* true if operator returns set */
	PGOid opcollid;     /* OID of collation of result */
	PGOid inputcollid;  /* OID of collation that operator should use */
	PGList *args;       /* arguments to the operator (1 or 2) */
	int location;       /* token location, or -1 if unknown */
} PGOpExpr;

/*
 * DistinctExpr - expression node for "x IS DISTINCT FROM y"
 *
 * Except for the nodetag, this is represented identically to an PGOpExpr
 * 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 PGOpExpr DistinctExpr;

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

/*
 * PGScalarArrayOpExpr - 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 PGScalarArrayOpExpr {
	PGExpr xpr;
	PGOid opno;        /* PG_OPERATOR OID of the operator */
	PGOid opfuncid;    /* PG_PROC OID of underlying function */
	bool useOr;        /* true for ANY, false for ALL */
	PGOid inputcollid; /* OID of collation that operator should use */
	PGList *args;      /* the scalar and array operands */
	int location;      /* token location, or -1 if unknown */
} PGScalarArrayOpExpr;

/*
 * PGBoolExpr - 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 PGBoolExprType { PG_AND_EXPR, PG_OR_EXPR, PG_NOT_EXPR } PGBoolExprType;

typedef struct PGBoolExpr {
	PGExpr xpr;
	PGBoolExprType boolop;
	PGList *args; /* arguments to this expression */
	int location; /* token location, or -1 if unknown */
} PGBoolExpr;

/*
 * PGSubLink
 *
 * A PGSubLink 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:
 *	PG_EXISTS_SUBLINK		EXISTS(SELECT ...)
 *	PG_ALL_SUBLINK			(lefthand) op ALL (SELECT ...)
 *	PG_ANY_SUBLINK			(lefthand) op ANY (SELECT ...)
 *	PG_ROWCOMPARE_SUBLINK	(lefthand) op (SELECT ...)
 *	PG_EXPR_SUBLINK		(SELECT with single targetlist item ...)
 *	PG_MULTIEXPR_SUBLINK	(SELECT with multiple targetlist items ...)
 *	PG_ARRAY_SUBLINK		ARRAY(SELECT with single targetlist item ...)
 *	PG_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 PG_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.
 *
 * PGSubLink is classed as an PGExpr node, but it is not actually executable;
 * it must be replaced in the expression tree by a PGSubPlan 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 PG_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 PG_PARAM_MULTIEXPR Params appearing elsewhere in the tlist.
 *
 * The PG_CTE_SUBLINK case never occurs in actual PGSubLink nodes, but it is used
 * in SubPlans generated for WITH subqueries.
 */
typedef enum PGSubLinkType {
	PG_EXISTS_SUBLINK,
	PG_ALL_SUBLINK,
	PG_ANY_SUBLINK,
	PG_ROWCOMPARE_SUBLINK,
	PG_EXPR_SUBLINK,
	PG_MULTIEXPR_SUBLINK,
	PG_ARRAY_SUBLINK,
	PG_CTE_SUBLINK /* for SubPlans only */
} PGSubLinkType;

typedef struct PGSubLink {
	PGExpr xpr;
	PGSubLinkType subLinkType; /* see above */
	int subLinkId;             /* ID (1..n); 0 if not MULTIEXPR */
	PGNode *testexpr;          /* outer-query test for ALL/ANY/ROWCOMPARE */
	PGList *operName;          /* originally specified operator name */
	PGNode *subselect;         /* subselect as PGQuery* or raw parsetree */
	int location;              /* token location, or -1 if unknown */
} PGSubLink;

/*
 * PGSubPlan - executable expression node for a subplan (sub-SELECT)
 *
 * The planner replaces PGSubLink nodes in expression trees with PGSubPlan
 * nodes after it has finished planning the subquery.  PGSubPlan 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
 * (PGOpExpr, an AND/OR tree of OpExprs, or PGRowCompareExpr) for the combining
 * operator(s); the left-hand arguments are the original lefthand expressions,
 * and the right-hand arguments are PG_PARAM_EXEC PGParam 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 PGSubLink node, but the PG_PARAM_SUBLINK nodes are replaced by
 * suitably numbered PG_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 PGSubPlan
 * 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 PG_PARAM_EXEC params indexed by parParam
 * (the parParam and args lists must have the same ordering).  setParam is a
 * list of the PG_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 PGSubPlan {
	PGExpr xpr;
	/* Fields copied from original PGSubLink: */
	PGSubLinkType subLinkType; /* see above */
	/* The combining operators, transformed to an executable expression: */
	PGNode *testexpr; /* PGOpExpr or PGRowCompareExpr expression tree */
	PGList *paramIds; /* IDs of Params embedded in the above */
	/* Identification of the PGPlan tree to use: */
	int plan_id; /* PGIndex (from 1) in PlannedStmt.subplans */
	/* Identification of the PGSubPlan for EXPLAIN and debugging purposes: */
	char *plan_name; /* A name assigned during planning */
	/* Extra data useful for determining subplan's output type: */
	PGOid firstColType;      /* Type of first column of subplan result */
	int32_t firstColTypmod;  /* Typmod of first column of subplan result */
	PGOid 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) */
	PGList *setParam; /* initplan subqueries have to set these
								 * Params for parent plan */
	PGList *parParam; /* indices of input Params from parent plan */
	PGList *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 */
} PGSubPlan;

/*
 * PGAlternativeSubPlan - expression node for a choice among SubPlans
 *
 * The subplans are given as a PGList 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 PGAlternativeSubPlan {
	PGExpr xpr;
	PGList *subplans; /* SubPlan(s) with equivalent results */
} PGAlternativeSubPlan;

/* ----------------
 * PGFieldSelect
 *
 * PGFieldSelect 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 PGFieldSelect {
	PGExpr xpr;
	PGExpr *arg;           /* input expression */
	PGAttrNumber fieldnum; /* attribute number of field to extract */
	PGOid resulttype;      /* type of the field (result type of this
								 * node) */
	int32_t resulttypmod;  /* output typmod (usually -1) */
	PGOid resultcollid;    /* OID of collation of the field */
} PGFieldSelect;

/* ----------------
 * PGFieldStore
 *
 * PGFieldStore 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 PGArrayRef, this is used to implement UPDATE of a
 * portion of a column.
 *
 * A single PGFieldStore 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 PGFieldStore {
	PGExpr xpr;
	PGExpr *arg;       /* input tuple value */
	PGList *newvals;   /* new value(s) for field(s) */
	PGList *fieldnums; /* integer list of field attnums */
	PGOid resulttype;  /* type of result (same as type of arg) */
	                   /* Like PGRowExpr, we deliberately omit a typmod and collation here */
} PGFieldStore;

/* ----------------
 * PGRelabelType
 *
 * PGRelabelType 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 PGRelabelType {
	PGExpr xpr;
	PGExpr *arg;                  /* input expression */
	PGOid resulttype;             /* output type of coercion expression */
	int32_t resulttypmod;         /* output typmod (usually -1) */
	PGOid resultcollid;           /* OID of collation, or InvalidOid if none */
	PGCoercionForm relabelformat; /* how to display this node */
	int location;                 /* token location, or -1 if unknown */
} PGRelabelType;

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

/* ----------------
 * PGArrayCoerceExpr
 *
 * PGArrayCoerceExpr represents a type coercion from one array type to another,
 * which is implemented by applying the indicated element-type coercion
 * function to each element of the source array.  If elemfuncid is InvalidOid
 * then the element types are binary-compatible, but the coercion still
 * requires some effort (we have to fix the element type ID stored in the
 * array header).
 * ----------------
 */

typedef struct PGArrayCoerceExpr {
	PGExpr xpr;
	PGExpr *arg;                 /* input expression (yields an array) */
	PGOid elemfuncid;            /* OID of element coercion function, or 0 */
	PGOid resulttype;            /* output type of coercion (an array type) */
	int32_t resulttypmod;        /* output typmod (also element typmod) */
	PGOid resultcollid;          /* OID of collation, or InvalidOid if none */
	bool isExplicit;             /* conversion semantics flag to pass to func */
	PGCoercionForm coerceformat; /* how to display this node */
	int location;                /* token location, or -1 if unknown */
} PGArrayCoerceExpr;

/* ----------------
 * PGConvertRowtypeExpr
 *
 * PGConvertRowtypeExpr 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.
 * ----------------
 */

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

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

/*----------
 * PGCaseExpr - 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
 *		PGCaseTestExpr '=' compexpr
 * where the PGCaseTestExpr 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 PGCaseExpr has been through parse analysis
 * yet by checking whether casetype is InvalidOid or not.
 *----------
 */
typedef struct PGCaseExpr {
	PGExpr xpr;
	PGOid casetype;    /* type of expression result */
	PGOid casecollid;  /* OID of collation, or InvalidOid if none */
	PGExpr *arg;       /* implicit equality comparison argument */
	PGList *args;      /* the arguments (list of WHEN clauses) */
	PGExpr *defresult; /* the default result (ELSE clause) */
	int location;      /* token location, or -1 if unknown */
} PGCaseExpr;

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

/*
 * Placeholder node for the test value to be processed by a CASE expression.
 * This is effectively like a PGParam, but can be implemented more simply
 * since we need only one replacement value at a time.
 *
 * We also use this in nested UPDATE expressions.
 * See transformAssignmentIndirection().
 */
typedef struct PGCaseTestExpr {
	PGExpr xpr;
	PGOid typeId;    /* type for substituted value */
	int32_t typeMod; /* typemod for substituted value */
	PGOid collation; /* collation for the substituted value */
} PGCaseTestExpr;

/*
 * PGArrayExpr - 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 PGArrayExpr {
	PGExpr xpr;
	PGOid array_typeid;   /* type of expression result */
	PGOid array_collid;   /* OID of collation, or InvalidOid if none */
	PGOid element_typeid; /* common type of array elements */
	PGList *elements;     /* the array elements or sub-arrays */
	bool multidims;       /* true if elements are sub-arrays */
	int location;         /* token location, or -1 if unknown */
} PGArrayExpr;

/*
 * PGRowExpr - 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 PGRowExpr 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 PGRowExpr
 * was created by expanding a whole-row Var.  This is so that we can retain
 * the column alias names of the RTE that the PGVar 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 PGRowExpr {
	PGExpr xpr;
	PGList *args;     /* the fields */
	PGOid row_typeid; /* RECORDOID or a composite type's ID */

	/*
	 * 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 PGRowExpr node.
	 *
	 * We don't need to store a collation either.  The result type is
	 * necessarily composite, and composite types never have a collation.
	 */
	PGCoercionForm row_format; /* how to display this node */
	PGList *colnames;          /* list of String, or NIL */
	int location;              /* token location, or -1 if unknown */
} PGRowExpr;

/*
 * PGRowCompareExpr - 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 PGRowCompareExpr 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
 * PGRowCompareType enum for the convenience of parser logic.
 */
typedef enum PGRowCompareType {
	/* Values of this enum are chosen to match btree strategy numbers */
	PG_ROWCOMPARE_LT = 1, /* BTLessStrategyNumber */
	PG_ROWCOMPARE_LE = 2, /* BTLessEqualStrategyNumber */
	PG_ROWCOMPARE_EQ = 3, /* BTEqualStrategyNumber */
	PG_ROWCOMPARE_GE = 4, /* BTGreaterEqualStrategyNumber */
	PG_ROWCOMPARE_GT = 5, /* BTGreaterStrategyNumber */
	PG_ROWCOMPARE_NE = 6  /* no such btree strategy */
} PGRowCompareType;

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

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

/*
 * PGMinMaxExpr - a GREATEST or LEAST function
 */
typedef enum PGMinMaxOp { PG_IS_GREATEST, IS_LEAST } PGMinMaxOp;

typedef struct PGMinMaxExpr {
	PGExpr xpr;
	PGOid minmaxtype;   /* common type of arguments and result */
	PGOid minmaxcollid; /* OID of collation of result */
	PGOid inputcollid;  /* OID of collation that function should use */
	PGMinMaxOp op;      /* function to execute */
	PGList *args;       /* the arguments */
	int location;       /* token location, or -1 if unknown */
} PGMinMaxExpr;

/*
 * PGSQLValueFunction - 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 PGSQLValueFunctionOp {
	PG_SVFOP_CURRENT_DATE,
	PG_SVFOP_CURRENT_TIME,
	PG_SVFOP_CURRENT_TIME_N,
	PG_SVFOP_CURRENT_TIMESTAMP,
	PG_SVFOP_CURRENT_TIMESTAMP_N,
	PG_SVFOP_LOCALTIME,
	PG_SVFOP_LOCALTIME_N,
	PG_SVFOP_LOCALTIMESTAMP,
	PG_SVFOP_LOCALTIMESTAMP_N,
	PG_SVFOP_CURRENT_ROLE,
	PG_SVFOP_CURRENT_USER,
	PG_SVFOP_USER,
	PG_SVFOP_SESSION_USER,
	PG_SVFOP_CURRENT_CATALOG,
	PG_SVFOP_CURRENT_SCHEMA
} PGSQLValueFunctionOp;

typedef struct PGSQLValueFunction {
	PGExpr xpr;
	PGSQLValueFunctionOp op; /* which function this is */
	PGOid type;              /* result type/typmod */
	int32_t typmod;
	int location; /* token location, or -1 if unknown */
} PGSQLValueFunction;

/* ----------------
 * PGNullTest
 *
 * PGNullTest 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 PGNullTestType { PG_IS_NULL, IS_NOT_NULL } PGNullTestType;

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

/*
 * PGBooleanTest
 *
 * PGBooleanTest 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 PGBoolTestType {
	PG_IS_TRUE,
	IS_NOT_TRUE,
	IS_FALSE,
	IS_NOT_FALSE,
	IS_UNKNOWN,
	IS_NOT_UNKNOWN
} PGBoolTestType;

typedef struct PGBooleanTest {
	PGExpr xpr;
	PGExpr *arg;                 /* input expression */
	PGBoolTestType booltesttype; /* test type */
	int location;                /* token location, or -1 if unknown */
} PGBooleanTest;

/*
 * PGCoerceToDomain
 *
 * PGCoerceToDomain 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
 * PGRelabelType in the scenario where no constraints are applied.
 */
typedef struct PGCoerceToDomain {
	PGExpr xpr;
	PGExpr *arg;                   /* input expression */
	PGOid resulttype;              /* domain type ID (result type) */
	int32_t resulttypmod;          /* output typmod (currently always -1) */
	PGOid resultcollid;            /* OID of collation, or InvalidOid if none */
	PGCoercionForm coercionformat; /* how to display this node */
	int location;                  /* token location, or -1 if unknown */
} PGCoerceToDomain;

/*
 * Placeholder node for the value to be processed by a domain's check
 * constraint.  This is effectively like a PGParam, 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 PGCoerceToDomainValue {
	PGExpr xpr;
	PGOid typeId;    /* type for substituted value */
	int32_t typeMod; /* typemod for substituted value */
	PGOid collation; /* collation for the substituted value */
	int location;    /* token location, or -1 if unknown */
} PGCoerceToDomainValue;

/*
 * 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 PGSetToDefault {
	PGExpr xpr;
	PGOid typeId;    /* type for substituted value */
	int32_t typeMod; /* typemod for substituted value */
	PGOid collation; /* collation for the substituted value */
	int location;    /* token location, or -1 if unknown */
} PGSetToDefault;

/*
 * PGNode representing [WHERE] CURRENT OF cursor_name
 *
 * CURRENT OF is a bit like a PGVar, 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 PGCurrentOfExpr {
	PGExpr xpr;
	PGIndex cvarno;    /* RT index of target relation */
	char *cursor_name; /* name of referenced cursor, or NULL */
	int cursor_param;  /* refcursor parameter number, or 0 */
} PGCurrentOfExpr;

/*
 * PGNextValueExpr - 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 PGNextValueExpr {
	PGExpr xpr;
	PGOid seqid;
	PGOid typeId;
} PGNextValueExpr;

/*
 * PGInferenceElem - 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 PGInferenceElem {
	PGExpr xpr;
	PGNode *expr;       /* expression to infer from, or NULL */
	PGOid infercollid;  /* OID of collation, or InvalidOid */
	PGOid inferopclass; /* OID of att opclass, or InvalidOid */
} PGInferenceElem;

/*--------------------
 * PGTargetEntry -
 *	   a target entry (used in query target lists)
 *
 * Strictly speaking, a PGTargetEntry 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 PGSortGroupClause 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 PGTargetEntry {
	PGExpr xpr;
	PGExpr *expr;            /* expression to evaluate */
	PGAttrNumber resno;      /* attribute number (see notes above) */
	char *resname;           /* name of the column (could be NULL) */
	PGIndex ressortgroupref; /* nonzero if referenced by a sort/group
									 * clause */
	PGOid resorigtbl;        /* OID of column's source table */
	PGAttrNumber resorigcol; /* column's number in source table */
	bool resjunk;            /* set to true to eliminate the attribute from
								 * final target list */
} PGTargetEntry;

/* ----------------------------------------------------------------
 *					node types for join trees
 *
 * The leaves of a join tree structure are PGRangeTblRef nodes.  Above
 * these, PGJoinExpr nodes can appear to denote a specific kind of join
 * or qualified join.  Also, PGFromExpr nodes can appear to denote an
 * ordinary cross-product join ("FROM foo, bar, baz WHERE ...").
 * PGFromExpr is like a PGJoinExpr of jointype PG_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 PGJoinExpr 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 PGRangeVar,
 * PGRangeSubselect, and PGRangeFunction nodes, which are all replaced by
 * PGRangeTblRef nodes during the parse analysis phase.  Also, the top-level
 * PGFromExpr is added during parse analysis; the grammar regards FROM and
 * WHERE as separate.
 * ----------------------------------------------------------------
 */

/*
 * PGRangeTblRef - 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 PGRangeTblRef {
	PGNodeTag type;
	int rtindex;
} PGRangeTblRef;

/*----------
 * PGJoinExpr - 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 PGAlias 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 PGJoin, 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 PGJoinExpr {
	PGNodeTag type;
	PGJoinType jointype; /* type of join */
	bool isNatural;      /* Natural join? Will need to shape table */
	PGNode *larg;        /* left subtree */
	PGNode *rarg;        /* right subtree */
	PGList *usingClause; /* USING clause, if any (list of String) */
	PGNode *quals;       /* qualifiers on join, if any */
	PGAlias *alias;      /* user-written alias clause, if any */
	int rtindex;         /* RT index assigned for join, or 0 */
	int location;          /* token location, or -1 if unknown */
} PGJoinExpr;

/*----------
 * PGFromExpr - represents a FROM ... WHERE ... construct
 *
 * This is both more flexible than a PGJoinExpr (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 PGFromExpr {
	PGNodeTag type;
	PGList *fromlist; /* PGList of join subtrees */
	PGNode *quals;    /* qualifiers on join, if any */
} PGFromExpr;

/*----------
 * PGOnConflictExpr - 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 PGOnConflictExpr {
	PGNodeTag type;
	PGOnConflictAction action; /* DO NOTHING or UPDATE? */

	/* Arbiter */
	PGList *arbiterElems; /* unique index arbiter list (of
								 * InferenceElem's) */
	PGNode *arbiterWhere; /* unique index arbiter WHERE clause */
	PGOid constraint;     /* pg_constraint OID for arbiter */

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

}