path: root/src/include/nodes/primnodes.h

/*-------------------------------------------------------------------------
 *
 * 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) 1996-2012, 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/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;

typedef enum InhOption
{
	INH_NO,						/* Do NOT scan child tables */
	INH_YES,					/* DO scan child tables */
	INH_DEFAULT					/* Use current SQL_inheritance option */
} InhOption;

/* 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 inhOpt shows 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 */
	InhOption	inhOpt;			/* 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;

/*
 * IntoClause - target information for SELECT INTO and CREATE TABLE AS
 */
typedef struct IntoClause
{
	NodeTag		type;

	RangeVar   *rel;			/* target relation name */
	List	   *colNames;		/* column names to assign, or NIL */
	List	   *options;		/* options from WITH clause */
	OnCommitAction onCommit;	/* what do we do at COMMIT? */
	char	   *tableSpaceName; /* table space to use, or NULL */
	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)
 *
 * Note: during parsing/planning, varnoold/varoattno are always just copies
 * of varno/varattno.  At the tail 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.  But varnoold/varoattno continue to 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 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 */
	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		varnoold;		/* original value of varno, for debugging */
	AttrNumber	varoattno;		/* original value of varattno */
	int			location;		/* token location, or -1 if unknown */
} Var;

/*
 * Const
 */
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.)
 *
 * Note: currently, paramtypmod is valid for PARAM_SUBLINK Params, and for
 * PARAM_EXEC Params generated from them; it is always -1 for PARAM_EXTERN
 * params, since the APIs that supply values for such parameters don't carry
 * any typmod info.
 * ----------------
 */
typedef enum ParamKind
{
	PARAM_EXTERN,
	PARAM_EXEC,
	PARAM_SUBLINK
} 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
 * (before Postgres 9.0 it was just bare expressions).	The non-resjunk TLEs
 * 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.
 */
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 */
	List	   *args;			/* arguments and sort expressions */
	List	   *aggorder;		/* ORDER BY (list of SortGroupClause) */
	List	   *aggdistinct;	/* DISTINCT (list of SortGroupClause) */
	bool		aggstar;		/* TRUE if argument list was really '*' */
	Index		agglevelsup;	/* > 0 if agg belongs to outer query */
	int			location;		/* token location, or -1 if unknown */
} Aggref;

/*
 * 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 */
	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;

/* ----------------
 *	ArrayRef: describes an array subscripting operation
 *
 * An ArrayRef 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.
 *
 * 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.
 * ----------------
 */
typedef struct ArrayRef
{
	Expr		xpr;
	Oid			refarraytype;	/* type of the array proper */
	Oid			refelemtype;	/* type of the array elements */
	int32		reftypmod;		/* typmod of the array (and elements too) */
	Oid			refcollid;		/* OID of collation, or InvalidOid if none */
	List	   *refupperindexpr;/* expressions that evaluate to upper array
								 * indexes */
	List	   *reflowerindexpr;/* expressions that evaluate to lower array
								 * indexes */
	Expr	   *refexpr;		/* the expression that evaluates to an array
								 * value */
	Expr	   *refassgnexpr;	/* expression for the source value, or NULL if
								 * fetch */
} ArrayRef;

/*
 * 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_EXPLICIT			/* explicit cast operation */
} CoercionContext;

/*
 * CoercionForm - information showing how to display a function-call node
 */
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_DONTCARE				/* special case for planner */
} 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 */
	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, the executor can
 * handle any number of arguments.	The parser generally treats AND and OR
 * as binary and so it typically only produces two-element lists, but the
 * optimizer will flatten trees of AND and OR nodes to produce longer lists
 * when possible.  There are also a few special cases where more arguments
 * can appear before optimization.
 */
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 ...)
 *	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).  Note that both
 * ROWCOMPARE and EXPR require the subselect to deliver only one row.
 * 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, and ARRAY SubLinks, testexpr and operName are unused and
 * are always null.
 *
 * 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,
	ARRAY_SUBLINK,
	CTE_SUBLINK					/* for SubPlans only */
} SubLinkType;


typedef struct SubLink
{
	Expr		xpr;
	SubLinkType subLinkType;	/* see above */
	Node	   *testexpr;		/* outer-query test for ALL/ANY/ROWCOMPARE */
	List	   *operName;		/* originally specified operator name */
	Node	   *subselect;		/* subselect as Query* or 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 */
	/* 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
 *
 * 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 ArrayRef, this is used to implement UPDATE of a
 * portion of a column.
 *
 * 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 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 ArrayCoerceExpr
{
	Expr		xpr;
	Expr	   *arg;			/* input expression (yields an array) */
	Oid			elemfuncid;		/* OID of element coercion function, or 0 */
	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 */
	bool		isExplicit;		/* conversion semantics flag to pass to func */
	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.
 * ----------------
 */

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 use this in nested UPDATE expressions.
 * See transformAssignmentIndirection().
 */
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 */

	/*
	 * 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;

/*
 * 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 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.
 *
 * NOTE: the semantics of this for rowtype inputs are noticeably different
 * from the scalar case.  We provide an "argisrow" flag to reflect that.
 * ----------------
 */

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 if input is of a composite type */
} 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 */
} 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;

/*--------------------
 * 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;

#endif   /* PRIMNODES_H */