text: /*-------------------------------------------------------------------------
   *
   * 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) 1996-2022, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   * src/include/nodes/primnodes.h
   *
   *-------------------------------------------------------------------------
   */
  #ifndef PRIMNODES_H
  #define PRIMNODES_H
  
  #include "access/attnum.h"
  #include "nodes/bitmapset.h"
  #include "nodes/pg_list.h"
  
  
  /* ----------------------------------------------------------------
   *						node definitions
   * ----------------------------------------------------------------
   */
  
  /*
   * Alias -
   *	  specifies an alias for a range variable; the alias might also
   *	  specify renaming of columns within the table.
   *
   * Note: colnames is a list of String nodes.  In Alias structs
   * associated with RTEs, there may be entries corresponding to dropped
   * columns; these are normally empty strings ("").  See parsenodes.h for info.
   */
  typedef struct Alias
  {
  	NodeTag		type;
  	char	   *aliasname;		/* aliased rel name (never qualified) */
  	List	   *colnames;		/* optional list of column aliases */
  } Alias;
  
  /* What to do at commit time for temporary relations */
  typedef enum OnCommitAction
  {
  	ONCOMMIT_NOOP,				/* No ON COMMIT clause (do nothing) */
  	ONCOMMIT_PRESERVE_ROWS,		/* ON COMMIT PRESERVE ROWS (do nothing) */
  	ONCOMMIT_DELETE_ROWS,		/* ON COMMIT DELETE ROWS */
  	ONCOMMIT_DROP				/* ON COMMIT DROP */
  } OnCommitAction;
  
  /*
   * RangeVar - range variable, used in FROM clauses
   *
   * Also used to represent table names in utility statements; there, the alias
   * field is not used, and inh tells whether to apply the operation
   * recursively to child tables.  In some contexts it is also useful to carry
   * a TEMP table indication here.
   */
  typedef struct RangeVar
  {
  	NodeTag		type;
  	char	   *catalogname;	/* the catalog (database) name, or NULL */
  	char	   *schemaname;		/* the schema name, or NULL */
  	char	   *relname;		/* the relation/sequence name */
  	bool		inh;			/* expand rel by inheritance? recursively act
  								 * on children? */
  	char		relpersistence; /* see RELPERSISTENCE_* in pg_class.h */
  	Alias	   *alias;			/* table alias & optional column aliases */
  	int			location;		/* token location, or -1 if unknown */
  } RangeVar;
  
  typedef enum TableFuncType
  {
  	TFT_XMLTABLE,
  	TFT_JSON_TABLE
  } TableFuncType;
  
  /*
   * TableFunc - node for a table function, such as XMLTABLE or JSON_TABLE.
   *
   * Entries in the ns_names list are either String nodes containing
   * literal namespace names, or NULL pointers to represent DEFAULT.
   */
  typedef struct TableFunc
  {
  	NodeTag		type;
  	TableFuncType functype;		/* XMLTABLE or JSON_TABLE */
  	List	   *ns_uris;		/* list of namespace URI expressions */
  	List	   *ns_names;		/* list of namespace names or NULL */
  	Node	   *docexpr;		/* input document expression */
  	Node	   *rowexpr;		/* row filter expression */
  	List	   *colnames;		/* column names (list of String) */
  	List	   *coltypes;		/* OID list of column type OIDs */
  	List	   *coltypmods;		/* integer list of column typmods */
  	List	   *colcollations;	/* OID list of column collation OIDs */
  	List	   *colexprs;		/* list of column filter expressions */
  	List	   *coldefexprs;	/* list of column default expressions */
  	List	   *colvalexprs;	/* list of column value expressions */
  	Bitmapset  *notnulls;		/* nullability flag for each output column */
  	Node	   *plan;			/* JSON_TABLE plan */
  	int			ordinalitycol;	/* counts from 0; -1 if none specified */
  	int			location;		/* token location, or -1 if unknown */
  } TableFunc;
  
  /*
   * IntoClause - target information for SELECT INTO, CREATE TABLE AS, and
   * CREATE MATERIALIZED VIEW
   *
   * For CREATE MATERIALIZED VIEW, viewQuery is the parsed-but-not-rewritten
   * SELECT Query for the view; otherwise it's NULL.  (Although it's actually
   * Query*, we declare it as Node* to avoid a forward reference.)
   */
  typedef struct IntoClause
  {
  	NodeTag		type;
  
  	RangeVar   *rel;			/* target relation name */
  	List	   *colNames;		/* column names to assign, or NIL */
  	char	   *accessMethod;	/* table access method */
  	List	   *options;		/* options from WITH clause */
  	OnCommitAction onCommit;	/* what do we do at COMMIT? */
  	char	   *tableSpaceName; /* table space to use, or NULL */
  	Node	   *viewQuery;		/* materialized view's SELECT query */
  	bool		skipData;		/* true for WITH NO DATA */
  } IntoClause;
  
  
  /* ----------------------------------------------------------------
   *					node types for executable expressions
   * ----------------------------------------------------------------
   */
  
  /*
   * Expr - generic superclass for executable-expression nodes
   *
   * All node types that are used in executable expression trees should derive
   * from Expr (that is, have Expr as their first field).  Since Expr only
   * contains NodeTag, this is a formality, but it is an easy form of
   * documentation.  See also the ExprState node types in execnodes.h.
   */
  typedef struct Expr
  {
  	NodeTag		type;
  } Expr;
  
  /*
   * Var - expression node representing a variable (ie, a table column)
   *
   * In the parser and planner, varno and varattno identify the semantic
   * referent, which is a base-relation column unless the reference is to a join
   * USING column that isn't semantically equivalent to either join input column
   * (because it is a FULL join or the input column requires a type coercion).
   * In those cases varno and varattno refer to the JOIN RTE.  (Early in the
   * planner, we replace such join references by the implied expression; but up
   * till then we want join reference Vars to keep their original identity for
   * query-printing purposes.)
   *
   * At the end of planning, Var nodes appearing in upper-level plan nodes are
   * reassigned to point to the outputs of their subplans; for example, in a
   * join node varno becomes INNER_VAR or OUTER_VAR and varattno becomes the
   * index of the proper element of that subplan's target list.  Similarly,
   * INDEX_VAR is used to identify Vars that reference an index column rather
   * than a heap column.  (In ForeignScan and CustomScan plan nodes, INDEX_VAR
   * is abused to signify references to columns of a custom scan tuple type.)
   *
   * ROWID_VAR is used in the planner to identify nonce variables that carry
   * row identity information during UPDATE/DELETE.  This value should never
   * be seen outside the planner.
   *
   * In the parser, varnosyn and varattnosyn are either identical to
   * varno/varattno, or they specify the column's position in an aliased JOIN
   * RTE that hides the semantic referent RTE's refname.  This is a syntactic
   * identifier as opposed to the semantic identifier; it tells ruleutils.c
   * how to print the Var properly.  varnosyn/varattnosyn retain their values
   * throughout planning and execution, so they are particularly helpful to
   * identify Vars when debugging.  Note, however, that a Var that is generated
   * in the planner and doesn't correspond to any simple relation column may
   * have varnosyn = varattnosyn = 0.
   */
  #define    INNER_VAR		(-1)	/* reference to inner subplan */
  #define    OUTER_VAR		(-2)	/* reference to outer subplan */
  #define    INDEX_VAR		(-3)	/* reference to index column */
  #define    ROWID_VAR		(-4)	/* row identity column during planning */
  
  #define IS_SPECIAL_VARNO(varno)		((int) (varno) < 0)
  
  /* 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;
  	int			varno;			/* index of this var's relation in the range
  								 * table, or INNER_VAR/OUTER_VAR/etc */
  	AttrNumber	varattno;		/* attribute number of this var, or zero for
  								 * all attrs ("whole-row Var") */
  	Oid			vartype;		/* pg_type OID for the type of this var */
  	int32		vartypmod;		/* pg_attribute typmod value */
  	Oid			varcollid;		/* OID of collation, or InvalidOid if none */
  	Index		varlevelsup;	/* for subquery variables referencing outer
  								 * relations; 0 in a normal var, >0 means N
  								 * levels up */
  	Index		varnosyn;		/* syntactic relation index (0 if unknown) */
  	AttrNumber	varattnosyn;	/* syntactic attribute number */
  	int			location;		/* token location, or -1 if unknown */
  } Var;
  
  /*
   * Const
   *
   * Note: for varlena data types, we make a rule that a Const node's value
   * must be in non-extended form (4-byte header, no compression or external
   * references).  This ensures that the Const node is self-contained and makes
   * it more likely that equal() will see logically identical values as equal.
   */
  typedef struct Const
  {
  	Expr		xpr;
  	Oid			consttype;		/* pg_type OID of the constant's datatype */
  	int32		consttypmod;	/* typmod value, if any */
  	Oid			constcollid;	/* OID of collation, or InvalidOid if none */
  	int			constlen;		/* typlen of the constant's datatype */
  	Datum		constvalue;		/* the constant's value */
  	bool		constisnull;	/* whether the constant is null (if true,
  								 * constvalue is undefined) */
  	bool		constbyval;		/* whether this datatype is passed by value.
  								 * If true, then all the information is stored
  								 * in the Datum. If false, then the Datum
  								 * contains a pointer to the information. */
  	int			location;		/* token location, or -1 if unknown */
  } Const;
  
  /*
   * Param
   *
   *		paramkind specifies the kind of parameter. The possible values
   *		for this field are:
   *
   *		PARAM_EXTERN:  The parameter value is supplied from outside the plan.
   *				Such parameters are numbered from 1 to n.
   *
   *		PARAM_EXEC:  The parameter is an internal executor parameter, used
   *				for passing values into and out of sub-queries or from
   *				nestloop joins to their inner scans.
   *				For historical reasons, such parameters are numbered from 0.
   *				These numbers are independent of PARAM_EXTERN numbers.
   *
   *		PARAM_SUBLINK:	The parameter represents an output column of a SubLink
   *				node's sub-select.  The column number is contained in the
   *				`paramid' field.  (This type of Param is converted to
   *				PARAM_EXEC during planning.)
   *
   *		PARAM_MULTIEXPR:  Like PARAM_SUBLINK, the parameter represents an
   *				output column of a SubLink node's sub-select, but here, the
   *				SubLink is always a MULTIEXPR SubLink.  The high-order 16 bits
   *				of the `paramid' field contain the SubLink's subLinkId, and
   *				the low-order 16 bits contain the column number.  (This type
   *				of Param is also converted to PARAM_EXEC during planning.)
   */
  typedef enum ParamKind
  {
  	PARAM_EXTERN,
  	PARAM_EXEC,
  	PARAM_SUBLINK,
  	PARAM_MULTIEXPR
  } ParamKind;
  
  typedef struct Param
  {
  	Expr		xpr;
  	ParamKind	paramkind;		/* kind of parameter. See above */
  	int			paramid;		/* numeric ID for parameter */
  	Oid			paramtype;		/* pg_type OID of parameter's datatype */
  	int32		paramtypmod;	/* typmod value, if known */
  	Oid			paramcollid;	/* OID of collation, or InvalidOid if none */
  	int			location;		/* token location, or -1 if unknown */
  } Param;
  
  /*
   * Aggref
   *
   * The aggregate's args list is a targetlist, ie, a list of TargetEntry nodes.
   *
   * For a normal (non-ordered-set) aggregate, the non-resjunk TargetEntries
   * represent the aggregate's regular arguments (if any) and resjunk TLEs can
   * be added at the end to represent ORDER BY expressions that are not also
   * arguments.  As in a top-level Query, the TLEs can be marked with
   * ressortgroupref indexes to let them be referenced by SortGroupClause
   * entries in the aggorder and/or aggdistinct lists.  This represents ORDER BY
   * and DISTINCT operations to be applied to the aggregate input rows before
   * they are passed to the transition function.  The grammar only allows a
   * simple "DISTINCT" specifier for the arguments, but we use the full
   * query-level representation to allow more code sharing.
   *
   * For an ordered-set aggregate, the args list represents the WITHIN GROUP
   * (aggregated) arguments, all of which will be listed in the aggorder list.
   * DISTINCT is not supported in this case, so aggdistinct will be NIL.
   * The direct arguments appear in aggdirectargs (as a list of plain
   * expressions, not TargetEntry nodes).
   *
   * aggtranstype is the data type of the state transition values for this
   * aggregate (resolved to an actual type, if agg's transtype is polymorphic).
   * This is determined during planning and is InvalidOid before that.
   *
   * aggargtypes is an OID list of the data types of the direct and regular
   * arguments.  Normally it's redundant with the aggdirectargs and args lists,
   * but in a combining aggregate, it's not because the args list has been
   * replaced with a single argument representing the partial-aggregate
   * transition values.
   *
   * aggsplit indicates the expected partial-aggregation mode for the Aggref's
   * parent plan node.  It's always set to AGGSPLIT_SIMPLE in the parser, but
   * the planner might change it to something else.  We use this mainly as
   * a crosscheck that the Aggrefs match the plan; but note that when aggsplit
   * indicates a non-final mode, aggtype reflects the transition data type
   * not the SQL-level output type of the aggregate.
   *
   * aggno and aggtransno are -1 in the parse stage, and are set in planning.
   * Aggregates with the same 'aggno' represent the same aggregate expression,
   * and can share the result.  Aggregates with same 'transno' but different
   * 'aggno' can share the same transition state, only the final function needs
   * to be called separately.
   */
  typedef struct Aggref
  {
  	Expr		xpr;
  	Oid			aggfnoid;		/* pg_proc Oid of the aggregate */
  	Oid			aggtype;		/* type Oid of result of the aggregate */
  	Oid			aggcollid;		/* OID of collation of result */
  	Oid			inputcollid;	/* OID of collation that function should use */
  	Oid			aggtranstype;	/* type Oid of aggregate's transition value */
  	List	   *aggargtypes;	/* type Oids of direct and aggregated args */
  	List	   *aggdirectargs;	/* direct arguments, if an ordered-set agg */
  	List	   *args;			/* aggregated arguments and sort expressions */
  	List	   *aggorder;		/* ORDER BY (list of SortGroupClause) */
  	List	   *aggdistinct;	/* DISTINCT (list of SortGroupClause) */
  	Expr	   *aggfilter;		/* FILTER expression, if any */
  	bool		aggstar;		/* true if argument list was really '*' */
  	bool		aggvariadic;	/* true if variadic arguments have been
  								 * combined into an array last argument */
  	char		aggkind;		/* aggregate kind (see pg_aggregate.h) */
  	Index		agglevelsup;	/* > 0 if agg belongs to outer query */
  	AggSplit	aggsplit;		/* expected agg-splitting mode of parent Agg */
  	int			aggno;			/* unique ID within the Agg node */
  	int			aggtransno;		/* unique ID of transition state in the Agg */
  	int			location;		/* token location, or -1 if unknown */
  } Aggref;
  
  /*
   * GroupingFunc
   *
   * A GroupingFunc is a GROUPING(...) expression, which behaves in many ways
   * like an aggregate function (e.g. it "belongs" to a specific query level,
   * which might not be the one immediately containing it), but also differs in
   * an important respect: it never evaluates its arguments, they merely
   * designate expressions from the GROUP BY clause of the query level to which
   * it belongs.
   *
   * The spec defines the evaluation of GROUPING() purely by syntactic
   * replacement, but we make it a real expression for optimization purposes so
   * that one Agg node can handle multiple grouping sets at once.  Evaluating the
   * result only needs the column positions to check against the grouping set
   * being projected.  However, for EXPLAIN to produce meaningful output, we have
   * to keep the original expressions around, since expression deparse does not
   * give us any feasible way to get at the GROUP BY clause.
   *
   * Also, we treat two GroupingFunc nodes as equal if they have equal arguments
   * lists and agglevelsup, without comparing the refs and cols annotations.
   *
   * In raw parse output we have only the args list; parse analysis fills in the
   * refs list, and the planner fills in the cols list.
   */
  typedef struct GroupingFunc
  {
  	Expr		xpr;
  	List	   *args;			/* arguments, not evaluated but kept for
  								 * benefit of EXPLAIN etc. */
  	List	   *refs;			/* ressortgrouprefs of arguments */
  	List	   *cols;			/* actual column positions set by planner */
  	Index		agglevelsup;	/* same as Aggref.agglevelsup */
  	int			location;		/* token location */
  } GroupingFunc;
  
  /*
   * WindowFunc
   */
  typedef struct WindowFunc
  {
  	Expr		xpr;
  	Oid			winfnoid;		/* pg_proc Oid of the function */
  	Oid			wintype;		/* type Oid of result of the window function */
  	Oid			wincollid;		/* OID of collation of result */
  	Oid			inputcollid;	/* OID of collation that function should use */
  	List	   *args;			/* arguments to the window function */
  	Expr	   *aggfilter;		/* FILTER expression, if any */
  	Index		winref;			/* index of associated WindowClause */
  	bool		winstar;		/* true if argument list was really '*' */
  	bool		winagg;			/* is function a simple aggregate? */
  	int			location;		/* token location, or -1 if unknown */
  } WindowFunc;
  
  /*
   * SubscriptingRef: describes a subscripting operation over a container
   * (array, etc).
   *
   * A SubscriptingRef can describe fetching a single element from a container,
   * fetching a part of a container (e.g. an array slice), storing a single
   * element into a container, or storing a slice.  The "store" cases work with
   * an initial container value and a source value that is inserted into the
   * appropriate part of the container; the result of the operation is an
   * entire new modified container value.
   *
   * If reflowerindexpr = NIL, then we are fetching or storing a single container
   * element at the subscripts given by refupperindexpr. Otherwise we are
   * fetching or storing a container slice, that is a rectangular subcontainer
   * with lower and upper bounds given by the index expressions.
   * reflowerindexpr must be the same length as refupperindexpr when it
   * is not NIL.
   *
   * In the slice case, individual expressions in the subscript lists can be
   * NULL, meaning "substitute the array's current lower or upper bound".
   * (Non-array containers may or may not support this.)
   *
   * refcontainertype is the actual container type that determines the
   * subscripting semantics.  (This will generally be either the exposed type of
   * refexpr, or the base type if that is a domain.)  refelemtype is the type of
   * the container's elements; this is saved for the use of the subscripting
   * functions, but is not used by the core code.  refrestype, reftypmod, and
   * refcollid describe the type of the SubscriptingRef's result.  In a store
   * expression, refrestype will always match refcontainertype; in a fetch,
   * it could be refelemtype for an element fetch, or refcontainertype for a
   * slice fetch, or possibly something else as determined by type-specific
   * subscripting logic.  Likewise, reftypmod and refcollid will match the
   * container's properties in a store, but could be different in a fetch.
   *
   * Note: for the cases where a container is returned, if refexpr yields a R/W
   * expanded container, then the implementation is allowed to modify that
   * object in-place and return the same object.
   */
  typedef struct SubscriptingRef
  {
  	Expr		xpr;
  	Oid			refcontainertype;	/* type of the container proper */
  	Oid			refelemtype;	/* the container type's pg_type.typelem */
  	Oid			refrestype;		/* type of the SubscriptingRef's result */
  	int32		reftypmod;		/* typmod of the result */
  	Oid			refcollid;		/* collation of result, or InvalidOid if none */
  	List	   *refupperindexpr;	/* expressions that evaluate to upper
  									 * container indexes */
  	List	   *reflowerindexpr;	/* expressions that evaluate to lower
  									 * container indexes, or NIL for single
  									 * container element */
  	Expr	   *refexpr;		/* the expression that evaluates to a
  								 * container value */
  	Expr	   *refassgnexpr;	/* expression for the source value, or NULL if
  								 * fetch */
  } SubscriptingRef;
  
  /*
   * CoercionContext - distinguishes the allowed set of type casts
   *
   * NB: ordering of the alternatives is significant; later (larger) values
   * allow more casts than earlier ones.
   */
  typedef enum CoercionContext
  {
  	COERCION_IMPLICIT,			/* coercion in context of expression */
  	COERCION_ASSIGNMENT,		/* coercion in context of assignment */
  	COERCION_PLPGSQL,			/* if no assignment cast, use CoerceViaIO */
  	COERCION_EXPLICIT			/* explicit cast operation */
  } CoercionContext;
  
  /*
   * CoercionForm - how to display a FuncExpr or related node
   *
   * "Coercion" is a bit of a misnomer, since this value records other
   * special syntaxes besides casts, but for now we'll keep this naming.
   *
   * NB: equal() ignores CoercionForm fields, therefore this *must* not carry
   * any semantically significant information.  We need that behavior so that
   * the planner will consider equivalent implicit and explicit casts to be
   * equivalent.  In cases where those actually behave differently, the coercion
   * function's arguments will be different.
   */
  typedef enum CoercionForm
  {
  	COERCE_EXPLICIT_CALL,		/* display as a function call */
  	COERCE_EXPLICIT_CAST,		/* display as an explicit cast */
  	COERCE_IMPLICIT_CAST,		/* implicit cast, so hide it */
  	COERCE_SQL_SYNTAX			/* display with SQL-mandated special syntax */
  } CoercionForm;
  
  /*
   * FuncExpr - expression node for a function call
   */
  typedef struct FuncExpr
  {
  	Expr		xpr;
  	Oid			funcid;			/* PG_PROC OID of the function */
  	Oid			funcresulttype; /* PG_TYPE OID of result value */
  	bool		funcretset;		/* true if function returns set */
  	bool		funcvariadic;	/* true if variadic arguments have been
  								 * combined into an array last argument */
  	CoercionForm funcformat;	/* how to display this function call */
  	Oid			funccollid;		/* OID of collation of result */
  	Oid			inputcollid;	/* OID of collation that function should use */
  	List	   *args;			/* arguments to the function */
  	int			location;		/* token location, or -1 if unknown */
  } FuncExpr;
  
  /*
   * NamedArgExpr - a named argument of a function
   *
   * This node type can only appear in the args list of a FuncCall or FuncExpr
   * node.  We support pure positional call notation (no named arguments),
   * named notation (all arguments are named), and mixed notation (unnamed
   * arguments followed by named ones).
   *
   * Parse analysis sets argnumber to the positional index of the argument,
   * but doesn't rearrange the argument list.
   *
   * The planner will convert argument lists to pure positional notation
   * during expression preprocessing, so execution never sees a NamedArgExpr.
   */
  typedef struct NamedArgExpr
  {
  	Expr		xpr;
  	Expr	   *arg;			/* the argument expression */
  	char	   *name;			/* the name */
  	int			argnumber;		/* argument's number in positional notation */
  	int			location;		/* argument name location, or -1 if unknown */
  } NamedArgExpr;
  
  /*
   * OpExpr - expression node for an operator invocation
   *
   * Semantically, this is essentially the same as a function call.
   *
   * Note that opfuncid is not necessarily filled in immediately on creation
   * of the node.  The planner makes sure it is valid before passing the node
   * tree to the executor, but during parsing/planning opfuncid can be 0.
   */
  typedef struct OpExpr
  {
  	Expr		xpr;
  	Oid			opno;			/* PG_OPERATOR OID of the operator */
  	Oid			opfuncid;		/* PG_PROC OID of underlying function */
  	Oid			opresulttype;	/* PG_TYPE OID of result value */
  	bool		opretset;		/* true if operator returns set */
  	Oid			opcollid;		/* OID of collation of result */
  	Oid			inputcollid;	/* OID of collation that operator should use */
  	List	   *args;			/* arguments to the operator (1 or 2) */
  	int			location;		/* token location, or -1 if unknown */
  } OpExpr;
  
  /*
   * DistinctExpr - expression node for "x IS DISTINCT FROM y"
   *
   * Except for the nodetag, this is represented identically to an OpExpr
   * referencing the "=" operator for x and y.
   * We use "=", not the more obvious "<>", because more datatypes have "="
   * than "<>".  This means the executor must invert the operator result.
   * Note that the operator function won't be called at all if either input
   * is NULL, since then the result can be determined directly.
   */
  typedef OpExpr DistinctExpr;
  
  /*
   * NullIfExpr - a NULLIF expression
   *
   * Like DistinctExpr, this is represented the same as an OpExpr referencing
   * the "=" operator for x and y.
   */
  typedef OpExpr NullIfExpr;
  
  /*
   * ScalarArrayOpExpr - expression node for "scalar op ANY/ALL (array)"
   *
   * The operator must yield boolean.  It is applied to the left operand
   * and each element of the righthand array, and the results are combined
   * with OR or AND (for ANY or ALL respectively).  The node representation
   * is almost the same as for the underlying operator, but we need a useOr
   * flag to remember whether it's ANY or ALL, and we don't have to store
   * the result type (or the collation) because it must be boolean.
   *
   * A ScalarArrayOpExpr with a valid hashfuncid is evaluated during execution
   * by building a hash table containing the Const values from the RHS arg.
   * This table is probed during expression evaluation.  The planner will set
   * hashfuncid to the hash function which must be used to build and probe the
   * hash table.  The executor determines if it should use hash-based checks or
   * the more traditional means based on if the hashfuncid is set or not.
   *
   * When performing hashed NOT IN, the negfuncid will also be set to the
   * equality function which the hash table must use to build and probe the hash
   * table.  opno and opfuncid will remain set to the <> operator and its
   * corresponding function and won't be used during execution.  For
   * non-hashtable based NOT INs, negfuncid will be set to InvalidOid.  See
   * convert_saop_to_hashed_saop().
   */
  typedef struct ScalarArrayOpExpr
  {
  	Expr		xpr;
  	Oid			opno;			/* PG_OPERATOR OID of the operator */
  	Oid			opfuncid;		/* PG_PROC OID of comparison function */
  	Oid			hashfuncid;		/* PG_PROC OID of hash func or InvalidOid */
  	Oid			negfuncid;		/* PG_PROC OID of negator of opfuncid function
  								 * or InvalidOid.  See above */
  	bool		useOr;			/* true for ANY, false for ALL */
  	Oid			inputcollid;	/* OID of collation that operator should use */
  	List	   *args;			/* the scalar and array operands */
  	int			location;		/* token location, or -1 if unknown */
  } ScalarArrayOpExpr;
  
  /*
   * BoolExpr - expression node for the basic Boolean operators AND, OR, NOT
   *
   * Notice the arguments are given as a List.  For NOT, of course the list
   * must always have exactly one element.  For AND and OR, there can be two
   * or more arguments.
   */
  typedef enum BoolExprType
  {
  	AND_EXPR, OR_EXPR, NOT_EXPR
  } BoolExprType;
  
  typedef struct BoolExpr
  {
  	Expr		xpr;
  	BoolExprType boolop;
  	List	   *args;			/* arguments to this expression */
  	int			location;		/* token location, or -1 if unknown */
  } BoolExpr;
  
  /*
   * SubLink
   *
   * A SubLink represents a subselect appearing in an expression, and in some
   * cases also the combining operator(s) just above it.  The subLinkType
   * indicates the form of the expression represented:
   *	EXISTS_SUBLINK		EXISTS(SELECT ...)
   *	ALL_SUBLINK			(lefthand) op ALL (SELECT ...)
   *	ANY_SUBLINK			(lefthand) op ANY (SELECT ...)
   *	ROWCOMPARE_SUBLINK	(lefthand) op (SELECT ...)
   *	EXPR_SUBLINK		(SELECT with single targetlist item ...)
   *	MULTIEXPR_SUBLINK	(SELECT with multiple targetlist items ...)
   *	ARRAY_SUBLINK		ARRAY(SELECT with single targetlist item ...)
   *	CTE_SUBLINK			WITH query (never actually part of an expression)
   * For ALL, ANY, and ROWCOMPARE, the lefthand is a list of expressions of the
   * same length as the subselect's targetlist.  ROWCOMPARE will *always* have
   * a list with more than one entry; if the subselect has just one target
   * then the parser will create an EXPR_SUBLINK instead (and any operator
   * above the subselect will be represented separately).
   * ROWCOMPARE, EXPR, and MULTIEXPR require the subselect to deliver at most
   * one row (if it returns no rows, the result is NULL).
   * ALL, ANY, and ROWCOMPARE require the combining operators to deliver boolean
   * results.  ALL and ANY combine the per-row results using AND and OR
   * semantics respectively.
   * ARRAY requires just one target column, and creates an array of the target
   * column's type using any number of rows resulting from the subselect.
   *
   * SubLink is classed as an Expr node, but it is not actually executable;
   * it must be replaced in the expression tree by a SubPlan node during
   * planning.
   *
   * NOTE: in the raw output of gram.y, testexpr contains just the raw form
   * of the lefthand expression (if any), and operName is the String name of
   * the combining operator.  Also, subselect is a raw parsetree.  During parse
   * analysis, the parser transforms testexpr into a complete boolean expression
   * that compares the lefthand value(s) to PARAM_SUBLINK nodes representing the
   * output columns of the subselect.  And subselect is transformed to a Query.
   * This is the representation seen in saved rules and in the rewriter.
   *
   * In EXISTS, EXPR, MULTIEXPR, and ARRAY SubLinks, testexpr and operName
   * are unused and are always null.
   *
   * subLinkId is currently used only for MULTIEXPR SubLinks, and is zero in
   * other SubLinks.  This number identifies different multiple-assignment
   * subqueries within an UPDATE statement's SET list.  It is unique only
   * within a particular targetlist.  The output column(s) of the MULTIEXPR
   * are referenced by PARAM_MULTIEXPR Params appearing elsewhere in the tlist.
   *
   * The CTE_SUBLINK case never occurs in actual SubLink nodes, but it is used
   * in SubPlans generated for WITH subqueries.
   */
  typedef enum SubLinkType
  {
  	EXISTS_SUBLINK,
  	ALL_SUBLINK,
  	ANY_SUBLINK,
  	ROWCOMPARE_SUBLINK,
  	EXPR_SUBLINK,
  	MULTIEXPR_SUBLINK,
  	ARRAY_SUBLINK,
  	CTE_SUBLINK					/* for SubPlans only */
  } SubLinkType;
  
  
  typedef struct SubLink
  {
  	Expr		xpr;
  	SubLinkType subLinkType;	/* see above */
  	int			subLinkId;		/* ID (1..n); 0 if not MULTIEXPR */
  	Node	   *testexpr;		/* outer-query test for ALL/ANY/ROWCOMPARE */
  	List	   *operName;		/* originally specified operator name */
  	Node	   *subselect;		/* subselect as Query* or raw parsetree */
  	int			location;		/* token location, or -1 if unknown */
  } SubLink;
  
  /*
   * SubPlan - executable expression node for a subplan (sub-SELECT)
   *
   * The planner replaces SubLink nodes in expression trees with SubPlan
   * nodes after it has finished planning the subquery.  SubPlan references
   * a sub-plantree stored in the subplans list of the toplevel PlannedStmt.
   * (We avoid a direct link to make it easier to copy expression trees
   * without causing multiple processing of the subplan.)
   *
   * In an ordinary subplan, testexpr points to an executable expression
   * (OpExpr, an AND/OR tree of OpExprs, or RowCompareExpr) for the combining
   * operator(s); the left-hand arguments are the original lefthand expressions,
   * and the right-hand arguments are PARAM_EXEC Param nodes representing the
   * outputs of the sub-select.  (NOTE: runtime coercion functions may be
   * inserted as well.)  This is just the same expression tree as testexpr in
   * the original SubLink node, but the PARAM_SUBLINK nodes are replaced by
   * suitably numbered PARAM_EXEC nodes.
   *
   * If the sub-select becomes an initplan rather than a subplan, the executable
   * expression is part of the outer plan's expression tree (and the SubPlan
   * node itself is not, but rather is found in the outer plan's initPlan
   * list).  In this case testexpr is NULL to avoid duplication.
   *
   * The planner also derives lists of the values that need to be passed into
   * and out of the subplan.  Input values are represented as a list "args" of
   * expressions to be evaluated in the outer-query context (currently these
   * args are always just Vars, but in principle they could be any expression).
   * The values are assigned to the global PARAM_EXEC params indexed by parParam
   * (the parParam and args lists must have the same ordering).  setParam is a
   * list of the PARAM_EXEC params that are computed by the sub-select, if it
   * is an initplan; they are listed in order by sub-select output column
   * position.  (parParam and setParam are integer Lists, not Bitmapsets,
   * because their ordering is significant.)
   *
   * Also, the planner computes startup and per-call costs for use of the
   * SubPlan.  Note that these include the cost of the subquery proper,
   * evaluation of the testexpr if any, and any hashtable management overhead.
   */
  typedef struct SubPlan
  {
  	Expr		xpr;
  	/* Fields copied from original SubLink: */
  	SubLinkType subLinkType;	/* see above */
  	/* The combining operators, transformed to an executable expression: */
  	Node	   *testexpr;		/* OpExpr or RowCompareExpr expression tree */
  	List	   *paramIds;		/* IDs of Params embedded in the above */
  	/* Identification of the Plan tree to use: */
  	int			plan_id;		/* Index (from 1) in PlannedStmt.subplans */
  	/* Identification of the SubPlan for EXPLAIN and debugging purposes: */
  	char	   *plan_name;		/* A name assigned during planning */
  	/* Extra data useful for determining subplan's output type: */
  	Oid			firstColType;	/* Type of first column of subplan result */
  	int32		firstColTypmod; /* Typmod of first column of subplan result */
  	Oid			firstColCollation;	/* Collation of first column of subplan
  									 * result */
  	/* Information about execution strategy: */
  	bool		useHashTable;	/* true to store subselect output in a hash
  								 * table (implies we are doing "IN") */
  	bool		unknownEqFalse; /* true if it's okay to return FALSE when the
  								 * spec result is UNKNOWN; this allows much
  								 * simpler handling of null values */
  	bool		parallel_safe;	/* is the subplan parallel-safe? */
  	/* Note: parallel_safe does not consider contents of testexpr or args */
  	/* Information for passing params into and out of the subselect: */
  	/* setParam and parParam are lists of integers (param IDs) */
  	List	   *setParam;		/* initplan subqueries have to set these
  								 * Params for parent plan */
  	List	   *parParam;		/* indices of input Params from parent plan */
  	List	   *args;			/* exprs to pass as parParam values */
  	/* Estimated execution costs: */
  	Cost		startup_cost;	/* one-time setup cost */
  	Cost		per_call_cost;	/* cost for each subplan evaluation */
  } SubPlan;
  
  /*
   * AlternativeSubPlan - expression node for a choice among SubPlans
   *
   * This is used only transiently during planning: by the time the plan
   * reaches the executor, all AlternativeSubPlan nodes have been removed.
   *
   * The subplans are given as a List so that the node definition need not
   * change if there's ever more than two alternatives.  For the moment,
   * though, there are always exactly two; and the first one is the fast-start
   * plan.
   */
  typedef struct AlternativeSubPlan
  {
  	Expr		xpr;
  	List	   *subplans;		/* SubPlan(s) with equivalent results */
  } AlternativeSubPlan;
  
  /* ----------------
   * FieldSelect
   *
   * FieldSelect represents the operation of extracting one field from a tuple
   * value.  At runtime, the input expression is expected to yield a rowtype
   * Datum.  The specified field number is extracted and returned as a Datum.
   * ----------------
   */
  
  typedef struct FieldSelect
  {
  	Expr		xpr;
  	Expr	   *arg;			/* input expression */
  	AttrNumber	fieldnum;		/* attribute number of field to extract */
  	Oid			resulttype;		/* type of the field (result type of this
  								 * node) */
  	int32		resulttypmod;	/* output typmod (usually -1) */
  	Oid			resultcollid;	/* OID of collation of the field */
  } FieldSelect;
  
  /* ----------------
   * FieldStore
   *
   * FieldStore represents the operation of modifying one field in a tuple
   * value, yielding a new tuple value (the input is not touched!).  Like
   * the assign case of SubscriptingRef, this is used to implement UPDATE of a
   * portion of a column.
   *
   * resulttype is always a named composite type (not a domain).  To update
   * a composite domain value, apply CoerceToDomain to the FieldStore.
   *
   * A single FieldStore can actually represent updates of several different
   * fields.  The parser only generates FieldStores with single-element lists,
   * but the planner will collapse multiple updates of the same base column
   * into one FieldStore.
   * ----------------
   */
  
  typedef struct FieldStore
  {
  	Expr		xpr;
  	Expr	   *arg;			/* input tuple value */
  	List	   *newvals;		/* new value(s) for field(s) */
  	List	   *fieldnums;		/* integer list of field attnums */
  	Oid			resulttype;		/* type of result (same as type of arg) */
  	/* Like RowExpr, we deliberately omit a typmod and collation here */
  } FieldStore;
  
  /* ----------------
   * RelabelType
   *
   * RelabelType represents a "dummy" type coercion between two binary-
   * compatible datatypes, such as reinterpreting the result of an OID
   * expression as an int4.  It is a no-op at runtime; we only need it
   * to provide a place to store the correct type to be attributed to
   * the expression result during type resolution.  (We can't get away
   * with just overwriting the type field of the input expression node,
   * so we need a separate node to show the coercion's result type.)
   * ----------------
   */
  
  typedef struct RelabelType
  {
  	Expr		xpr;
  	Expr	   *arg;			/* input expression */
  	Oid			resulttype;		/* output type of coercion expression */
  	int32		resulttypmod;	/* output typmod (usually -1) */
  	Oid			resultcollid;	/* OID of collation, or InvalidOid if none */
  	CoercionForm relabelformat; /* how to display this node */
  	int			location;		/* token location, or -1 if unknown */
  } RelabelType;
  
  /* ----------------
   * CoerceViaIO
   *
   * CoerceViaIO represents a type coercion between two types whose textual
   * representations are compatible, implemented by invoking the source type's
   * typoutput function then the destination type's typinput function.
   * ----------------
   */
  
  typedef struct CoerceViaIO
  {
  	Expr		xpr;
  	Expr	   *arg;			/* input expression */
  	Oid			resulttype;		/* output type of coercion */
  	/* output typmod is not stored, but is presumed -1 */
  	Oid			resultcollid;	/* OID of collation, or InvalidOid if none */
  	CoercionForm coerceformat;	/* how to display this node */
  	int			location;		/* token location, or -1 if unknown */
  } CoerceViaIO;
  
  /* ----------------
   * ArrayCoerceExpr
   *
   * ArrayCoerceExpr represents a type coercion from one array type to another,
   * which is implemented by applying the per-element coercion expression
   * "elemexpr" to each element of the source array.  Within elemexpr, the
   * source element is represented by a CaseTestExpr node.  Note that even if
   * elemexpr is a no-op (that is, just CaseTestExpr + RelabelType), the
   * coercion still requires some effort: we have to fix the element type OID
   * stored in the array header.
   * ----------------
   */
  
  typedef struct ArrayCoerceExpr
  {
  	Expr		xpr;
  	Expr	   *arg;			/* input expression (yields an array) */
  	Expr	   *elemexpr;		/* expression representing per-element work */
  	Oid			resulttype;		/* output type of coercion (an array type) */
  	int32		resulttypmod;	/* output typmod (also element typmod) */
  	Oid			resultcollid;	/* OID of collation, or InvalidOid if none */
  	CoercionForm coerceformat;	/* how to display this node */
  	int			location;		/* token location, or -1 if unknown */
  } ArrayCoerceExpr;
  
  /* ----------------
   * ConvertRowtypeExpr
   *
   * ConvertRowtypeExpr represents a type coercion from one composite type
   * to another, where the source type is guaranteed to contain all the columns
   * needed for the destination type plus possibly others; the columns need not
   * be in the same positions, but are matched up by name.  This is primarily
   * used to convert a whole-row value of an inheritance child table into a
   * valid whole-row value of its parent table's rowtype.  Both resulttype
   * and the exposed type of "arg" must be named composite types (not domains).
   * ----------------
   */
  
  typedef struct ConvertRowtypeExpr
  {
  	Expr		xpr;
  	Expr	   *arg;			/* input expression */
  	Oid			resulttype;		/* output type (always a composite type) */
  	/* Like RowExpr, we deliberately omit a typmod and collation here */
  	CoercionForm convertformat; /* how to display this node */
  	int			location;		/* token location, or -1 if unknown */
  } ConvertRowtypeExpr;
  
  /*----------
   * CollateExpr - COLLATE
   *
   * The planner replaces CollateExpr with RelabelType during expression
   * preprocessing, so execution never sees a CollateExpr.
   *----------
   */
  typedef struct CollateExpr
  {
  	Expr		xpr;
  	Expr	   *arg;			/* input expression */
  	Oid			collOid;		/* collation's OID */
  	int			location;		/* token location, or -1 if unknown */
  } CollateExpr;
  
  /*----------
   * CaseExpr - a CASE expression
   *
   * We support two distinct forms of CASE expression:
   *		CASE WHEN boolexpr THEN expr [ WHEN boolexpr THEN expr ... ]
   *		CASE testexpr WHEN compexpr THEN expr [ WHEN compexpr THEN expr ... ]
   * These are distinguishable by the "arg" field being NULL in the first case
   * and the testexpr in the second case.
   *
   * In the raw grammar output for the second form, the condition expressions
   * of the WHEN clauses are just the comparison values.  Parse analysis
   * converts these to valid boolean expressions of the form
   *		CaseTestExpr '=' compexpr
   * where the CaseTestExpr node is a placeholder that emits the correct
   * value at runtime.  This structure is used so that the testexpr need be
   * evaluated only once.  Note that after parse analysis, the condition
   * expressions always yield boolean.
   *
   * Note: we can test whether a CaseExpr has been through parse analysis
   * yet by checking whether casetype is InvalidOid or not.
   *----------
   */
  typedef struct CaseExpr
  {
  	Expr		xpr;
  	Oid			casetype;		/* type of expression result */
  	Oid			casecollid;		/* OID of collation, or InvalidOid if none */
  	Expr	   *arg;			/* implicit equality comparison argument */
  	List	   *args;			/* the arguments (list of WHEN clauses) */
  	Expr	   *defresult;		/* the default result (ELSE clause) */
  	int			location;		/* token location, or -1 if unknown */
  } CaseExpr;
  
  /*
   * CaseWhen - one arm of a CASE expression
   */
  typedef struct CaseWhen
  {
  	Expr		xpr;
  	Expr	   *expr;			/* condition expression */
  	Expr	   *result;			/* substitution result */
  	int			location;		/* token location, or -1 if unknown */
  } CaseWhen;
  
  /*
   * Placeholder node for the test value to be processed by a CASE expression.
   * This is effectively like a Param, but can be implemented more simply
   * since we need only one replacement value at a time.
   *
   * We also abuse this node type for some other purposes, including:
   *	* Placeholder for the current array element value in ArrayCoerceExpr;
   *	  see build_coercion_expression().
   *	* Nested FieldStore/SubscriptingRef assignment expressions in INSERT/UPDATE;
   *	  see transformAssignmentIndirection().
   *
   * The uses in CaseExpr and ArrayCoerceExpr are safe only to the extent that
   * there is not any other CaseExpr or ArrayCoerceExpr between the value source
   * node and its child CaseTestExpr(s).  This is true in the parse analysis
   * output, but the planner's function-inlining logic has to be careful not to
   * break it.
   *
   * The nested-assignment-expression case is safe because the only node types
   * that can be above such CaseTestExprs are FieldStore and SubscriptingRef.
   */
  typedef struct CaseTestExpr
  {
  	Expr		xpr;
  	Oid			typeId;			/* type for substituted value */
  	int32		typeMod;		/* typemod for substituted value */
  	Oid			collation;		/* collation for the substituted value */
  } CaseTestExpr;
  
  /*
   * ArrayExpr - an ARRAY[] expression
   *
   * Note: if multidims is false, the constituent expressions all yield the
   * scalar type identified by element_typeid.  If multidims is true, the
   * constituent expressions all yield arrays of element_typeid (ie, the same
   * type as array_typeid); at runtime we must check for compatible subscripts.
   */
  typedef struct ArrayExpr
  {
  	Expr		xpr;
  	Oid			array_typeid;	/* type of expression result */
  	Oid			array_collid;	/* OID of collation, or InvalidOid if none */
  	Oid			element_typeid; /* common type of array elements */
  	List	   *elements;		/* the array elements or sub-arrays */
  	bool		multidims;		/* true if elements are sub-arrays */
  	int			location;		/* token location, or -1 if unknown */
  } ArrayExpr;
  
  /*
   * RowExpr - a ROW() expression
   *
   * Note: the list of fields must have a one-for-one correspondence with
   * physical fields of the associated rowtype, although it is okay for it
   * to be shorter than the rowtype.  That is, the N'th list element must
   * match up with the N'th physical field.  When the N'th physical field
   * is a dropped column (attisdropped) then the N'th list element can just
   * be a NULL constant.  (This case can only occur for named composite types,
   * not RECORD types, since those are built from the RowExpr itself rather
   * than vice versa.)  It is important not to assume that length(args) is
   * the same as the number of columns logically present in the rowtype.
   *
   * colnames provides field names if the ROW() result is of type RECORD.
   * Names *must* be provided if row_typeid is RECORDOID; but if it is a
   * named composite type, colnames will be ignored in favor of using the
   * type's cataloged field names, so colnames should be NIL.  Like the
   * args list, colnames is defined to be one-for-one with physical fields
   * of the rowtype (although dropped columns shouldn't appear in the
   * RECORD case, so this fine point is currently moot).
   */
  typedef struct RowExpr
  {
  	Expr		xpr;
  	List	   *args;			/* the fields */
  	Oid			row_typeid;		/* RECORDOID or a composite type's ID */
  
  	/*
  	 * row_typeid cannot be a domain over composite, only plain composite.  To
  	 * create a composite domain value, apply CoerceToDomain to the RowExpr.
  	 *
  	 * Note: we deliberately do NOT store a typmod.  Although a typmod will be
  	 * associated with specific RECORD types at runtime, it will differ for
  	 * different backends, and so cannot safely be stored in stored
  	 * parsetrees.  We must assume typmod -1 for a RowExpr node.
  	 *
  	 * We don't need to store a collation either.  The result type is
  	 * necessarily composite, and composite types never have a collation.
  	 */
  	CoercionForm row_format;	/* how to display this node */
  	List	   *colnames;		/* list of String, or NIL */
  	int			location;		/* token location, or -1 if unknown */
  } RowExpr;
  
  /*
   * RowCompareExpr - row-wise comparison, such as (a, b) <= (1, 2)
   *
   * We support row comparison for any operator that can be determined to
   * act like =, <>, <, <=, >, or >= (we determine this by looking for the
   * operator in btree opfamilies).  Note that the same operator name might
   * map to a different operator for each pair of row elements, since the
   * element datatypes can vary.
   *
   * A RowCompareExpr node is only generated for the < <= > >= cases;
   * the = and <> cases are translated to simple AND or OR combinations
   * of the pairwise comparisons.  However, we include = and <> in the
   * RowCompareType enum for the convenience of parser logic.
   */
  typedef enum RowCompareType
  {
  	/* Values of this enum are chosen to match btree strategy numbers */
  	ROWCOMPARE_LT = 1,			/* BTLessStrategyNumber */
  	ROWCOMPARE_LE = 2,			/* BTLessEqualStrategyNumber */
  	ROWCOMPARE_EQ = 3,			/* BTEqualStrategyNumber */
  	ROWCOMPARE_GE = 4,			/* BTGreaterEqualStrategyNumber */
  	ROWCOMPARE_GT = 5,			/* BTGreaterStrategyNumber */
  	ROWCOMPARE_NE = 6			/* no such btree strategy */
  } RowCompareType;
  
  typedef struct RowCompareExpr
  {
  	Expr		xpr;
  	RowCompareType rctype;		/* LT LE GE or GT, never EQ or NE */
  	List	   *opnos;			/* OID list of pairwise comparison ops */
  	List	   *opfamilies;		/* OID list of containing operator families */
  	List	   *inputcollids;	/* OID list of collations for comparisons */
  	List	   *largs;			/* the left-hand input arguments */
  	List	   *rargs;			/* the right-hand input arguments */
  } RowCompareExpr;
  
  /*
   * CoalesceExpr - a COALESCE expression
   */
  typedef struct CoalesceExpr
  {
  	Expr		xpr;
  	Oid			coalescetype;	/* type of expression result */
  	Oid			coalescecollid; /* OID of collation, or InvalidOid if none */
  	List	   *args;			/* the arguments */
  	int			location;		/* token location, or -1 if unknown */
  } CoalesceExpr;
  
  /*
   * MinMaxExpr - a GREATEST or LEAST function
   */
  typedef enum MinMaxOp
  {
  	IS_GREATEST,
  	IS_LEAST
  } MinMaxOp;
  
  typedef struct MinMaxExpr
  {
  	Expr		xpr;
  	Oid			minmaxtype;		/* common type of arguments and result */
  	Oid			minmaxcollid;	/* OID of collation of result */
  	Oid			inputcollid;	/* OID of collation that function should use */
  	MinMaxOp	op;				/* function to execute */
  	List	   *args;			/* the arguments */
  	int			location;		/* token location, or -1 if unknown */
  } MinMaxExpr;
  
  /*
   * SQLValueFunction - parameterless functions with special grammar productions
   *
   * The SQL standard categorizes some of these as <datetime value function>
   * and others as <general value specification>.  We call 'em SQLValueFunctions
   * for lack of a better term.  We store type and typmod of the result so that
   * some code doesn't need to know each function individually, and because
   * we would need to store typmod anyway for some of the datetime functions.
   * Note that currently, all variants return non-collating datatypes, so we do
   * not need a collation field; also, all these functions are stable.
   */
  typedef enum SQLValueFunctionOp
  {
  	SVFOP_CURRENT_DATE,
  	SVFOP_CURRENT_TIME,
  	SVFOP_CURRENT_TIME_N,
  	SVFOP_CURRENT_TIMESTAMP,
  	SVFOP_CURRENT_TIMESTAMP_N,
  	SVFOP_LOCALTIME,
  	SVFOP_LOCALTIME_N,
  	SVFOP_LOCALTIMESTAMP,
  	SVFOP_LOCALTIMESTAMP_N,
  	SVFOP_CURRENT_ROLE,
  	SVFOP_CURRENT_USER,
  	SVFOP_USER,
  	SVFOP_SESSION_USER,
  	SVFOP_CURRENT_CATALOG,
  	SVFOP_CURRENT_SCHEMA
  } SQLValueFunctionOp;
  
  typedef struct SQLValueFunction
  {
  	Expr		xpr;
  	SQLValueFunctionOp op;		/* which function this is */
  	Oid			type;			/* result type/typmod */
  	int32		typmod;
  	int			location;		/* token location, or -1 if unknown */
  } SQLValueFunction;
  
  /*
   * XmlExpr - various SQL/XML functions requiring special grammar productions
   *
   * 'name' carries the "NAME foo" argument (already XML-escaped).
   * 'named_args' and 'arg_names' represent an xml_attribute list.
   * 'args' carries all other arguments.
   *
   * Note: result type/typmod/collation are not stored, but can be deduced
   * from the XmlExprOp.  The type/typmod fields are just used for display
   * purposes, and are NOT necessarily the true result type of the node.
   */
  typedef enum XmlExprOp
  {
  	IS_XMLCONCAT,				/* XMLCONCAT(args) */
  	IS_XMLELEMENT,				/* XMLELEMENT(name, xml_attributes, args) */
  	IS_XMLFOREST,				/* XMLFOREST(xml_attributes) */
  	IS_XMLPARSE,				/* XMLPARSE(text, is_doc, preserve_ws) */
  	IS_XMLPI,					/* XMLPI(name [, args]) */
  	IS_XMLROOT,					/* XMLROOT(xml, version, standalone) */
  	IS_XMLSERIALIZE,			/* XMLSERIALIZE(is_document, xmlval) */
  	IS_DOCUMENT					/* xmlval IS DOCUMENT */
  } XmlExprOp;
  
  typedef enum XmlOptionType
  {
  	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 String values */
  	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;
  
  /*
   * JsonExprOp -
   *		enumeration of JSON functions using JSON path
   */
  typedef enum JsonExprOp
  {
  	JSON_VALUE_OP,				/* JSON_VALUE() */
  	JSON_QUERY_OP,				/* JSON_QUERY() */
  	JSON_EXISTS_OP,				/* JSON_EXISTS() */
  	JSON_TABLE_OP               /* JSON_TABLE() */
  } JsonExprOp;
  
  /*
   * JsonEncoding -
   *		representation of JSON ENCODING clause
   */
  typedef enum JsonEncoding
  {
  	JS_ENC_DEFAULT,				/* unspecified */
  	JS_ENC_UTF8,
  	JS_ENC_UTF16,
  	JS_ENC_UTF32,
  } JsonEncoding;
  
  /*
   * JsonFormatType -
   *		enumeration of JSON formats used in JSON FORMAT clause
   */
  typedef enum JsonFormatType
  {
  	JS_FORMAT_DEFAULT,			/* unspecified */
  	JS_FORMAT_JSON,				/* FORMAT JSON [ENCODING ...] */
  	JS_FORMAT_JSONB				/* implicit internal format for RETURNING jsonb */
  } JsonFormatType;
  
  /*
   * JsonBehaviorType -
   *		enumeration of behavior types used in JSON ON ... BEHAVIOR clause
   *
   * 		If enum members are reordered, get_json_behavior() from ruleutils.c
   * 		must be updated accordingly.
   */
  typedef enum JsonBehaviorType
  {
  	JSON_BEHAVIOR_NULL = 0,
  	JSON_BEHAVIOR_ERROR,
  	JSON_BEHAVIOR_EMPTY,
  	JSON_BEHAVIOR_TRUE,
  	JSON_BEHAVIOR_FALSE,
  	JSON_BEHAVIOR_UNKNOWN,
  	JSON_BEHAVIOR_EMPTY_ARRAY,
  	JSON_BEHAVIOR_EMPTY_OBJECT,
  	JSON_BEHAVIOR_DEFAULT
  } JsonBehaviorType;
  
  /*
   * JsonWrapper -
   *		representation of WRAPPER clause for JSON_QUERY()
   */
  typedef enum JsonWrapper
  {
  	JSW_NONE,
  	JSW_CONDITIONAL,
  	JSW_UNCONDITIONAL,
  } JsonWrapper;
  
  /*
   * JsonFormat -
   *		representation of JSON FORMAT clause
   */
  typedef struct JsonFormat
  {
  	NodeTag		type;
  	JsonFormatType format_type;	/* format type */
  	JsonEncoding encoding;		/* JSON encoding */
  	int			location;		/* token location, or -1 if unknown */
  } JsonFormat;
  
  /*
   * JsonReturning -
   *		transformed representation of JSON RETURNING clause
   */
  typedef struct JsonReturning
  {
  	NodeTag		type;
  	JsonFormat *format;			/* output JSON format */
  	Oid			typid;			/* target type Oid */
  	int32		typmod;			/* target type modifier */
  } JsonReturning;
  
  /*
   * JsonValueExpr -
   *		representation of JSON value expression (expr [FORMAT json_format])
   */
  typedef struct JsonValueExpr
  {
  	NodeTag		type;
  	Expr	   *raw_expr;		/* raw expression */
  	Expr	   *formatted_expr;	/* formatted expression or NULL */
  	JsonFormat *format;			/* FORMAT clause, if specified */
  } JsonValueExpr;
  
  typedef enum JsonConstructorType
  {
  	JSCTOR_JSON_OBJECT = 1,
  	JSCTOR_JSON_ARRAY = 2,
  	JSCTOR_JSON_OBJECTAGG = 3,
  	JSCTOR_JSON_ARRAYAGG = 4,
  	JSCTOR_JSON_SCALAR = 5,
  	JSCTOR_JSON_SERIALIZE = 6,
  	JSCTOR_JSON_PARSE = 7
  } JsonConstructorType;
  
  /*
   * JsonConstructorExpr -
   *		wrapper over FuncExpr/Aggref/WindowFunc for SQL/JSON constructors
   */
  typedef struct JsonConstructorExpr
  {
  	Expr		xpr;
  	JsonConstructorType type;	/* constructor type */
  	List	   *args;
  	Expr	   *func;			/* underlying json[b]_xxx() function call */
  	Expr	   *coercion;		/* coercion to RETURNING type */
  	JsonReturning *returning;	/* RETURNING clause */
  	bool		absent_on_null;	/* ABSENT ON NULL? */
  	bool		unique;			/* WITH UNIQUE KEYS? (JSON_OBJECT[AGG] only) */
  	int			location;
  } JsonConstructorExpr;
  
  /*
   * JsonValueType -
   *		representation of JSON item type in IS JSON predicate
   */
  typedef enum JsonValueType
  {
  	JS_TYPE_ANY,				/* IS JSON [VALUE] */
  	JS_TYPE_OBJECT,				/* IS JSON OBJECT */
  	JS_TYPE_ARRAY,				/* IS JSON ARRAY*/
  	JS_TYPE_SCALAR				/* IS JSON SCALAR */
  } JsonValueType;
  
  /*
   * JsonIsPredicate -
   *		untransformed representation of IS JSON predicate
   */
  typedef struct JsonIsPredicate
  {
  	NodeTag		type;
  	Node	   *expr;			/* untransformed expression */
  	JsonFormat *format;			/* FORMAT clause, if specified */
  	JsonValueType value_type;	/* JSON item type */
  	bool		unique_keys;	/* check key uniqueness? */
  	int			location;		/* token location, or -1 if unknown */
  } JsonIsPredicate;
  
  /*
   * JsonBehavior -
   *		representation of JSON ON ... BEHAVIOR clause
   */
  typedef struct JsonBehavior
  {
  	NodeTag		type;
  	JsonBehaviorType btype;		/* behavior type */
  	Node	   *default_expr;	/* default expression, if any */
  } JsonBehavior;
  
  /*
   * JsonCoercion -
   *		coercion from SQL/JSON item types to SQL types
   */
  typedef struct JsonCoercion
  {
  	NodeTag		type;
  	Node	   *expr;			/* resulting expression coerced to target type */
  	bool		via_populate;	/* coerce result using json_populate_type()? */
  	bool		via_io;			/* coerce result using type input function? */
  	Oid			collation;		/* collation for coercion via I/O or populate */
  } JsonCoercion;
  
  /*
   * JsonItemCoercions -
   *		expressions for coercion from SQL/JSON item types directly to the
   *		output SQL type
   */
  typedef struct JsonItemCoercions
  {
  	NodeTag		type;
  	JsonCoercion *null;
  	JsonCoercion *string;
  	JsonCoercion *numeric;
  	JsonCoercion *boolean;
  	JsonCoercion *date;
  	JsonCoercion *time;
  	JsonCoercion *timetz;
  	JsonCoercion *timestamp;
  	JsonCoercion *timestamptz;
  	JsonCoercion *composite;	/* arrays and objects */
  } JsonItemCoercions;
  
  /*
   * JsonExpr -
   *		transformed representation of JSON_VALUE(), JSON_QUERY(), JSON_EXISTS()
   */
  typedef struct JsonExpr
  {
  	Expr		xpr;
  	JsonExprOp	op;				/* json function ID */
  	Node	   *formatted_expr;	/* formatted context item expression */
  	JsonCoercion *result_coercion;	/* resulting coercion to RETURNING type */
  	JsonFormat *format;			/* context item format (JSON/JSONB) */
  	Node	   *path_spec;		/* JSON path specification expression */
  	List	   *passing_names;	/* PASSING argument names */
  	List	   *passing_values;	/* PASSING argument values */
  	JsonReturning *returning;	/* RETURNING clause type/format info */
  	JsonBehavior *on_empty;		/* ON EMPTY behavior */
  	JsonBehavior *on_error;		/* ON ERROR behavior */
  	JsonItemCoercions *coercions; /* coercions for JSON_VALUE */
  	JsonWrapper	wrapper;		/* WRAPPER for JSON_QUERY */
  	bool		omit_quotes;	/* KEEP/OMIT QUOTES for JSON_QUERY */
  	int			location;		/* token location, or -1 if unknown */
  } JsonExpr;
  
  /*
   * JsonTableParent -
   *		transformed representation of parent JSON_TABLE plan node
   */
  typedef struct JsonTableParent
  {
  	NodeTag		type;
  	Const	   *path;		/* jsonpath constant */
  	char	   *name;		/* path name */
  	Node	   *child;		/* nested columns, if any */
  	bool		outerJoin;	/* outer or inner join for nested columns? */
  	int			colMin;		/* min column index in the resulting column list */
  	int			colMax;		/* max column index in the resulting column list */
  	bool		errorOnError; /* ERROR/EMPTY ON ERROR behavior */
  } JsonTableParent;
  
  /*
   * JsonTableSibling -
   *		transformed representation of joined sibling JSON_TABLE plan node
   */
  typedef struct JsonTableSibling
  {
  	NodeTag		type;
  	Node	   *larg;		/* left join node */
  	Node	   *rarg;		/* right join node */
  	bool		cross;		/* cross or union join? */
  } JsonTableSibling;
  
  /* ----------------
   * NullTest
   *
   * NullTest represents the operation of testing a value for NULLness.
   * The appropriate test is performed and returned as a boolean Datum.
   *
   * When argisrow is false, this simply represents a test for the null value.
   *
   * When argisrow is true, the input expression must yield a rowtype, and
   * the node implements "row IS [NOT] NULL" per the SQL standard.  This
   * includes checking individual fields for NULLness when the row datum
   * itself isn't NULL.
   *
   * NOTE: the combination of a rowtype input and argisrow==false does NOT
   * correspond to the SQL notation "row IS [NOT] NULL"; instead, this case
   * represents the SQL notation "row IS [NOT] DISTINCT FROM NULL".
   * ----------------
   */
  
  typedef enum NullTestType
  {
  	IS_NULL, IS_NOT_NULL
  } NullTestType;
  
  typedef struct NullTest
  {
  	Expr		xpr;
  	Expr	   *arg;			/* input expression */
  	NullTestType nulltesttype;	/* IS NULL, IS NOT NULL */
  	bool		argisrow;		/* T to perform field-by-field null checks */
  	int			location;		/* token location, or -1 if unknown */
  } NullTest;
  
  /*
   * BooleanTest
   *
   * BooleanTest represents the operation of determining whether a boolean
   * is TRUE, FALSE, or UNKNOWN (ie, NULL).  All six meaningful combinations
   * are supported.  Note that a NULL input does *not* cause a NULL result.
   * The appropriate test is performed and returned as a boolean Datum.
   */
  
  typedef enum BoolTestType
  {
  	IS_TRUE, IS_NOT_TRUE, IS_FALSE, IS_NOT_FALSE, IS_UNKNOWN, IS_NOT_UNKNOWN
  } BoolTestType;
  
  typedef struct BooleanTest
  {
  	Expr		xpr;
  	Expr	   *arg;			/* input expression */
  	BoolTestType booltesttype;	/* test type */
  	int			location;		/* token location, or -1 if unknown */
  } BooleanTest;
  
  /*
   * CoerceToDomain
   *
   * CoerceToDomain represents the operation of coercing a value to a domain
   * type.  At runtime (and not before) the precise set of constraints to be
   * checked will be determined.  If the value passes, it is returned as the
   * result; if not, an error is raised.  Note that this is equivalent to
   * RelabelType in the scenario where no constraints are applied.
   */
  typedef struct CoerceToDomain
  {
  	Expr		xpr;
  	Expr	   *arg;			/* input expression */
  	Oid			resulttype;		/* domain type ID (result type) */
  	int32		resulttypmod;	/* output typmod (currently always -1) */
  	Oid			resultcollid;	/* OID of collation, or InvalidOid if none */
  	CoercionForm coercionformat;	/* how to display this node */
  	int			location;		/* token location, or -1 if unknown */
  } CoerceToDomain;
  
  /*
   * Placeholder node for the value to be processed by a domain's check
   * constraint.  This is effectively like a Param, but can be implemented more
   * simply since we need only one replacement value at a time.
   *
   * Note: the typeId/typeMod/collation will be set from the domain's base type,
   * not the domain itself.  This is because we shouldn't consider the value
   * to be a member of the domain if we haven't yet checked its constraints.
   */
  typedef struct CoerceToDomainValue
  {
  	Expr		xpr;
  	Oid			typeId;			/* type for substituted value */
  	int32		typeMod;		/* typemod for substituted value */
  	Oid			collation;		/* collation for the substituted value */
  	int			location;		/* token location, or -1 if unknown */
  } CoerceToDomainValue;
  
  /*
   * Placeholder node for a DEFAULT marker in an INSERT or UPDATE command.
   *
   * This is not an executable expression: it must be replaced by the actual
   * column default expression during rewriting.  But it is convenient to
   * treat it as an expression node during parsing and rewriting.
   */
  typedef struct SetToDefault
  {
  	Expr		xpr;
  	Oid			typeId;			/* type for substituted value */
  	int32		typeMod;		/* typemod for substituted value */
  	Oid			collation;		/* collation for the substituted value */
  	int			location;		/* token location, or -1 if unknown */
  } SetToDefault;
  
  /*
   * Node representing [WHERE] CURRENT OF cursor_name
   *
   * CURRENT OF is a bit like a Var, in that it carries the rangetable index
   * of the target relation being constrained; this aids placing the expression
   * correctly during planning.  We can assume however that its "levelsup" is
   * always zero, due to the syntactic constraints on where it can appear.
   * Also, cvarno will always be a true RT index, never INNER_VAR etc.
   *
   * The referenced cursor can be represented either as a hardwired string
   * or as a reference to a run-time parameter of type REFCURSOR.  The latter
   * case is for the convenience of plpgsql.
   */
  typedef struct CurrentOfExpr
  {
  	Expr		xpr;
  	Index		cvarno;			/* RT index of target relation */
  	char	   *cursor_name;	/* name of referenced cursor, or NULL */
  	int			cursor_param;	/* refcursor parameter number, or 0 */
  } CurrentOfExpr;
  
  /*
   * NextValueExpr - get next value from sequence
   *
   * This has the same effect as calling the nextval() function, but it does not
   * check permissions on the sequence.  This is used for identity columns,
   * where the sequence is an implicit dependency without its own permissions.
   */
  typedef struct NextValueExpr
  {
  	Expr		xpr;
  	Oid			seqid;
  	Oid			typeId;
  } NextValueExpr;
  
  /*
   * InferenceElem - an element of a unique index inference specification
   *
   * This mostly matches the structure of IndexElems, but having a dedicated
   * primnode allows for a clean separation between the use of index parameters
   * by utility commands, and this node.
   */
  typedef struct InferenceElem
  {
  	Expr		xpr;
  	Node	   *expr;			/* expression to infer from, or NULL */
  	Oid			infercollid;	/* OID of collation, or InvalidOid */
  	Oid			inferopclass;	/* OID of att opclass, or InvalidOid */
  } InferenceElem;
  
  /*--------------------
   * TargetEntry -
   *	   a target entry (used in query target lists)
   *
   * Strictly speaking, a TargetEntry isn't an expression node (since it can't
   * be evaluated by ExecEvalExpr).  But we treat it as one anyway, since in
   * very many places it's convenient to process a whole query targetlist as a
   * single expression tree.
   *
   * In a SELECT's targetlist, resno should always be equal to the item's
   * ordinal position (counting from 1).  However, in an INSERT or UPDATE
   * targetlist, resno represents the attribute number of the destination
   * column for the item; so there may be missing or out-of-order resnos.
   * It is even legal to have duplicated resnos; consider
   *		UPDATE table SET arraycol[1] = ..., arraycol[2] = ..., ...
   * In an INSERT, the rewriter and planner will normalize the tlist by
   * reordering it into physical column order and filling in default values
   * for any columns not assigned values by the original query.  In an UPDATE,
   * after the rewriter merges multiple assignments for the same column, the
   * planner extracts the target-column numbers into a separate "update_colnos"
   * list, and then renumbers the tlist elements serially.  Thus, tlist resnos
   * match ordinal position in all tlists seen by the executor; but it is wrong
   * to assume that before planning has happened.
   *
   * 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.
   *
   * join_using_alias is an Alias node representing the join correlation
   * name that SQL:2016 and later allow to be attached to JOIN/USING.
   * Its column alias list includes only the common column names from USING,
   * and it does not restrict visibility of the join's input tables.
   *
   * 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) */
  	Alias	   *join_using_alias;	/* alias attached to USING clause, if any */
  	Node	   *quals;			/* qualifiers on join, if any */
  	Alias	   *alias;			/* user-written alias clause, if any */
  	int			rtindex;		/* RT index assigned for join, or 0 */
  } JoinExpr;
  
  /*----------
   * FromExpr - represents a FROM ... WHERE ... construct
   *
   * This is both more flexible than a JoinExpr (it can have any number of
   * children, including zero) and less so --- we don't need to deal with
   * aliases and so on.  The output column set is implicitly just the union
   * of the outputs of the children.
   *----------
   */
  typedef struct FromExpr
  {
  	NodeTag		type;
  	List	   *fromlist;		/* List of join subtrees */
  	Node	   *quals;			/* qualifiers on join, if any */
  } FromExpr;
  
  /*----------
   * OnConflictExpr - represents an ON CONFLICT DO ... expression
   *
   * The optimizer requires a list of inference elements, and optionally a WHERE
   * clause to infer a unique index.  The unique index (or, occasionally,
   * indexes) inferred are used to arbitrate whether or not the alternative ON
   * CONFLICT path is taken.
   *----------
   */
  typedef struct OnConflictExpr
  {
  	NodeTag		type;
  	OnConflictAction action;	/* DO NOTHING or UPDATE? */
  
  	/* Arbiter */
  	List	   *arbiterElems;	/* unique index arbiter list (of
  								 * InferenceElem's) */
  	Node	   *arbiterWhere;	/* unique index arbiter WHERE clause */
  	Oid			constraint;		/* pg_constraint OID for arbiter */
  
  	/* ON CONFLICT UPDATE */
  	List	   *onConflictSet;	/* List of ON CONFLICT SET TargetEntrys */
  	Node	   *onConflictWhere;	/* qualifiers to restrict UPDATE to */
  	int			exclRelIndex;	/* RT index of 'excluded' relation */
  	List	   *exclRelTlist;	/* tlist of the EXCLUDED pseudo relation */
  } OnConflictExpr;
  
  #endif							/* PRIMNODES_H */
  