postgresql/src/backend/parser/parse_agg.c

/*-------------------------------------------------------------------------
 *
 * parse_agg.c
 *	  handle aggregates and window functions in parser
 *
 * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/parser/parse_agg.c,v 1.94 2010/08/07 02:44:07 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "catalog/pg_constraint.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/tlist.h"
#include "optimizer/var.h"
#include "parser/parse_agg.h"
#include "parser/parse_clause.h"
#include "parser/parsetree.h"
#include "rewrite/rewriteManip.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"


typedef struct
{
	ParseState *pstate;
	Query	   *qry;
	List	   *groupClauses;
	bool		have_non_var_grouping;
	List	  **func_grouped_rels;
	int			sublevels_up;
} check_ungrouped_columns_context;

static void check_ungrouped_columns(Node *node, ParseState *pstate, Query *qry,
						List *groupClauses, bool have_non_var_grouping,
						List **func_grouped_rels);
static bool check_ungrouped_columns_walker(Node *node,
							   check_ungrouped_columns_context *context);


/*
 * transformAggregateCall -
 *		Finish initial transformation of an aggregate call
 *
 * parse_func.c has recognized the function as an aggregate, and has set up
 * all the fields of the Aggref except args, aggorder, aggdistinct and
 * agglevelsup.  The passed-in args list has been through standard expression
 * transformation, while the passed-in aggorder list hasn't been transformed
 * at all.
 *
 * Here we convert the args list into a targetlist by inserting TargetEntry
 * nodes, and then transform the aggorder and agg_distinct specifications to
 * produce lists of SortGroupClause nodes.	(That might also result in adding
 * resjunk expressions to the targetlist.)
 *
 * We must also determine which query level the aggregate actually belongs to,
 * set agglevelsup accordingly, and mark p_hasAggs true in the corresponding
 * pstate level.
 */
void
transformAggregateCall(ParseState *pstate, Aggref *agg,
					   List *args, List *aggorder, bool agg_distinct)
{
	List	   *tlist;
	List	   *torder;
	List	   *tdistinct = NIL;
	AttrNumber	attno;
	int			save_next_resno;
	int			min_varlevel;
	ListCell   *lc;

	/*
	 * Transform the plain list of Exprs into a targetlist.  We don't bother
	 * to assign column names to the entries.
	 */
	tlist = NIL;
	attno = 1;
	foreach(lc, args)
	{
		Expr	   *arg = (Expr *) lfirst(lc);
		TargetEntry *tle = makeTargetEntry(arg, attno++, NULL, false);

		tlist = lappend(tlist, tle);
	}

	/*
	 * If we have an ORDER BY, transform it.  This will add columns to the
	 * tlist if they appear in ORDER BY but weren't already in the arg list.
	 * They will be marked resjunk = true so we can tell them apart from
	 * regular aggregate arguments later.
	 *
	 * We need to mess with p_next_resno since it will be used to number any
	 * new targetlist entries.
	 */
	save_next_resno = pstate->p_next_resno;
	pstate->p_next_resno = attno;

	torder = transformSortClause(pstate,
								 aggorder,
								 &tlist,
								 true /* fix unknowns */ ,
								 true /* force SQL99 rules */ );

	/*
	 * If we have DISTINCT, transform that to produce a distinctList.
	 */
	if (agg_distinct)
	{
		tdistinct = transformDistinctClause(pstate, &tlist, torder, true);

		/*
		 * Remove this check if executor support for hashed distinct for
		 * aggregates is ever added.
		 */
		foreach(lc, tdistinct)
		{
			SortGroupClause *sortcl = (SortGroupClause *) lfirst(lc);

			if (!OidIsValid(sortcl->sortop))
			{
				Node	   *expr = get_sortgroupclause_expr(sortcl, tlist);

				ereport(ERROR,
						(errcode(ERRCODE_UNDEFINED_FUNCTION),
				errmsg("could not identify an ordering operator for type %s",
					   format_type_be(exprType(expr))),
						 errdetail("Aggregates with DISTINCT must be able to sort their inputs."),
						 parser_errposition(pstate, exprLocation(expr))));
			}
		}
	}

	/* Update the Aggref with the transformation results */
	agg->args = tlist;
	agg->aggorder = torder;
	agg->aggdistinct = tdistinct;

	pstate->p_next_resno = save_next_resno;

	/*
	 * The aggregate's level is the same as the level of the lowest-level
	 * variable or aggregate in its arguments; or if it contains no variables
	 * at all, we presume it to be local.
	 */
	min_varlevel = find_minimum_var_level((Node *) agg->args);

	/*
	 * An aggregate can't directly contain another aggregate call of the same
	 * level (though outer aggs are okay).	We can skip this check if we
	 * didn't find any local vars or aggs.
	 */
	if (min_varlevel == 0)
	{
		if (pstate->p_hasAggs &&
			checkExprHasAggs((Node *) agg->args))
			ereport(ERROR,
					(errcode(ERRCODE_GROUPING_ERROR),
					 errmsg("aggregate function calls cannot be nested"),
					 parser_errposition(pstate,
							   locate_agg_of_level((Node *) agg->args, 0))));
	}

	/* It can't contain window functions either */
	if (pstate->p_hasWindowFuncs &&
		checkExprHasWindowFuncs((Node *) agg->args))
		ereport(ERROR,
				(errcode(ERRCODE_GROUPING_ERROR),
				 errmsg("aggregate function calls cannot contain window function calls"),
				 parser_errposition(pstate,
									locate_windowfunc((Node *) agg->args))));

	if (min_varlevel < 0)
		min_varlevel = 0;
	agg->agglevelsup = min_varlevel;

	/* Mark the correct pstate as having aggregates */
	while (min_varlevel-- > 0)
		pstate = pstate->parentParseState;
	pstate->p_hasAggs = true;
}

/*
 * transformWindowFuncCall -
 *		Finish initial transformation of a window function call
 *
 * parse_func.c has recognized the function as a window function, and has set
 * up all the fields of the WindowFunc except winref.  Here we must (1) add
 * the WindowDef to the pstate (if not a duplicate of one already present) and
 * set winref to link to it; and (2) mark p_hasWindowFuncs true in the pstate.
 * Unlike aggregates, only the most closely nested pstate level need be
 * considered --- there are no "outer window functions" per SQL spec.
 */
void
transformWindowFuncCall(ParseState *pstate, WindowFunc *wfunc,
						WindowDef *windef)
{
	/*
	 * A window function call can't contain another one (but aggs are OK). XXX
	 * is this required by spec, or just an unimplemented feature?
	 */
	if (pstate->p_hasWindowFuncs &&
		checkExprHasWindowFuncs((Node *) wfunc->args))
		ereport(ERROR,
				(errcode(ERRCODE_WINDOWING_ERROR),
				 errmsg("window function calls cannot be nested"),
				 parser_errposition(pstate,
								  locate_windowfunc((Node *) wfunc->args))));

	/*
	 * If the OVER clause just specifies a window name, find that WINDOW
	 * clause (which had better be present).  Otherwise, try to match all the
	 * properties of the OVER clause, and make a new entry in the p_windowdefs
	 * list if no luck.
	 */
	if (windef->name)
	{
		Index		winref = 0;
		ListCell   *lc;

		Assert(windef->refname == NULL &&
			   windef->partitionClause == NIL &&
			   windef->orderClause == NIL &&
			   windef->frameOptions == FRAMEOPTION_DEFAULTS);

		foreach(lc, pstate->p_windowdefs)
		{
			WindowDef  *refwin = (WindowDef *) lfirst(lc);

			winref++;
			if (refwin->name && strcmp(refwin->name, windef->name) == 0)
			{
				wfunc->winref = winref;
				break;
			}
		}
		if (lc == NULL)			/* didn't find it? */
			ereport(ERROR,
					(errcode(ERRCODE_UNDEFINED_OBJECT),
					 errmsg("window \"%s\" does not exist", windef->name),
					 parser_errposition(pstate, windef->location)));
	}
	else
	{
		Index		winref = 0;
		ListCell   *lc;

		foreach(lc, pstate->p_windowdefs)
		{
			WindowDef  *refwin = (WindowDef *) lfirst(lc);

			winref++;
			if (refwin->refname && windef->refname &&
				strcmp(refwin->refname, windef->refname) == 0)
				 /* matched on refname */ ;
			else if (!refwin->refname && !windef->refname)
				 /* matched, no refname */ ;
			else
				continue;
			if (equal(refwin->partitionClause, windef->partitionClause) &&
				equal(refwin->orderClause, windef->orderClause) &&
				refwin->frameOptions == windef->frameOptions &&
				equal(refwin->startOffset, windef->startOffset) &&
				equal(refwin->endOffset, windef->endOffset))
			{
				/* found a duplicate window specification */
				wfunc->winref = winref;
				break;
			}
		}
		if (lc == NULL)			/* didn't find it? */
		{
			pstate->p_windowdefs = lappend(pstate->p_windowdefs, windef);
			wfunc->winref = list_length(pstate->p_windowdefs);
		}
	}

	pstate->p_hasWindowFuncs = true;
}

/*
 * parseCheckAggregates
 *	Check for aggregates where they shouldn't be and improper grouping.
 *
 *	Ideally this should be done earlier, but it's difficult to distinguish
 *	aggregates from plain functions at the grammar level.  So instead we
 *	check here.  This function should be called after the target list and
 *	qualifications are finalized.
 */
void
parseCheckAggregates(ParseState *pstate, Query *qry)
{
	List	   *groupClauses = NIL;
	bool		have_non_var_grouping;
	List	   *func_grouped_rels = NIL;
	ListCell   *l;
	bool		hasJoinRTEs;
	bool		hasSelfRefRTEs;
	PlannerInfo *root;
	Node	   *clause;

	/* This should only be called if we found aggregates or grouping */
	Assert(pstate->p_hasAggs || qry->groupClause || qry->havingQual);

	/*
	 * Scan the range table to see if there are JOIN or self-reference CTE
	 * entries.  We'll need this info below.
	 */
	hasJoinRTEs = hasSelfRefRTEs = false;
	foreach(l, pstate->p_rtable)
	{
		RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);

		if (rte->rtekind == RTE_JOIN)
			hasJoinRTEs = true;
		else if (rte->rtekind == RTE_CTE && rte->self_reference)
			hasSelfRefRTEs = true;
	}

	/*
	 * Aggregates must never appear in WHERE or JOIN/ON clauses.
	 *
	 * (Note this check should appear first to deliver an appropriate error
	 * message; otherwise we are likely to complain about some innocent
	 * variable in the target list, which is outright misleading if the
	 * problem is in WHERE.)
	 */
	if (checkExprHasAggs(qry->jointree->quals))
		ereport(ERROR,
				(errcode(ERRCODE_GROUPING_ERROR),
				 errmsg("aggregates not allowed in WHERE clause"),
				 parser_errposition(pstate,
							 locate_agg_of_level(qry->jointree->quals, 0))));
	if (checkExprHasAggs((Node *) qry->jointree->fromlist))
		ereport(ERROR,
				(errcode(ERRCODE_GROUPING_ERROR),
				 errmsg("aggregates not allowed in JOIN conditions"),
				 parser_errposition(pstate,
				 locate_agg_of_level((Node *) qry->jointree->fromlist, 0))));

	/*
	 * No aggregates allowed in GROUP BY clauses, either.
	 *
	 * While we are at it, build a list of the acceptable GROUP BY expressions
	 * for use by check_ungrouped_columns().
	 */
	foreach(l, qry->groupClause)
	{
		SortGroupClause *grpcl = (SortGroupClause *) lfirst(l);
		Node	   *expr;

		expr = get_sortgroupclause_expr(grpcl, qry->targetList);
		if (expr == NULL)
			continue;			/* probably cannot happen */
		if (checkExprHasAggs(expr))
			ereport(ERROR,
					(errcode(ERRCODE_GROUPING_ERROR),
					 errmsg("aggregates not allowed in GROUP BY clause"),
					 parser_errposition(pstate,
										locate_agg_of_level(expr, 0))));
		groupClauses = lcons(expr, groupClauses);
	}

	/*
	 * If there are join alias vars involved, we have to flatten them to the
	 * underlying vars, so that aliased and unaliased vars will be correctly
	 * taken as equal.	We can skip the expense of doing this if no rangetable
	 * entries are RTE_JOIN kind. We use the planner's flatten_join_alias_vars
	 * routine to do the flattening; it wants a PlannerInfo root node, which
	 * fortunately can be mostly dummy.
	 */
	if (hasJoinRTEs)
	{
		root = makeNode(PlannerInfo);
		root->parse = qry;
		root->planner_cxt = CurrentMemoryContext;
		root->hasJoinRTEs = true;

		groupClauses = (List *) flatten_join_alias_vars(root,
													  (Node *) groupClauses);
	}
	else
		root = NULL;			/* keep compiler quiet */

	/*
	 * Detect whether any of the grouping expressions aren't simple Vars; if
	 * they're all Vars then we don't have to work so hard in the recursive
	 * scans.  (Note we have to flatten aliases before this.)
	 */
	have_non_var_grouping = false;
	foreach(l, groupClauses)
	{
		if (!IsA((Node *) lfirst(l), Var))
		{
			have_non_var_grouping = true;
			break;
		}
	}

	/*
	 * Check the targetlist and HAVING clause for ungrouped variables.
	 *
	 * Note: because we check resjunk tlist elements as well as regular ones,
	 * this will also find ungrouped variables that came from ORDER BY and
	 * WINDOW clauses.	For that matter, it's also going to examine the
	 * grouping expressions themselves --- but they'll all pass the test ...
	 */
	clause = (Node *) qry->targetList;
	if (hasJoinRTEs)
		clause = flatten_join_alias_vars(root, clause);
	check_ungrouped_columns(clause, pstate, qry,
							groupClauses, have_non_var_grouping,
							&func_grouped_rels);

	clause = (Node *) qry->havingQual;
	if (hasJoinRTEs)
		clause = flatten_join_alias_vars(root, clause);
	check_ungrouped_columns(clause, pstate, qry,
							groupClauses, have_non_var_grouping,
							&func_grouped_rels);

	/*
	 * Per spec, aggregates can't appear in a recursive term.
	 */
	if (pstate->p_hasAggs && hasSelfRefRTEs)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_RECURSION),
				 errmsg("aggregate functions not allowed in a recursive query's recursive term"),
				 parser_errposition(pstate,
									locate_agg_of_level((Node *) qry, 0))));
}

/*
 * parseCheckWindowFuncs
 *	Check for window functions where they shouldn't be.
 *
 *	We have to forbid window functions in WHERE, JOIN/ON, HAVING, GROUP BY,
 *	and window specifications.	(Other clauses, such as RETURNING and LIMIT,
 *	have already been checked.)  Transformation of all these clauses must
 *	be completed already.
 */
void
parseCheckWindowFuncs(ParseState *pstate, Query *qry)
{
	ListCell   *l;

	/* This should only be called if we found window functions */
	Assert(pstate->p_hasWindowFuncs);

	if (checkExprHasWindowFuncs(qry->jointree->quals))
		ereport(ERROR,
				(errcode(ERRCODE_WINDOWING_ERROR),
				 errmsg("window functions not allowed in WHERE clause"),
				 parser_errposition(pstate,
								  locate_windowfunc(qry->jointree->quals))));
	if (checkExprHasWindowFuncs((Node *) qry->jointree->fromlist))
		ereport(ERROR,
				(errcode(ERRCODE_WINDOWING_ERROR),
				 errmsg("window functions not allowed in JOIN conditions"),
				 parser_errposition(pstate,
					  locate_windowfunc((Node *) qry->jointree->fromlist))));
	if (checkExprHasWindowFuncs(qry->havingQual))
		ereport(ERROR,
				(errcode(ERRCODE_WINDOWING_ERROR),
				 errmsg("window functions not allowed in HAVING clause"),
				 parser_errposition(pstate,
									locate_windowfunc(qry->havingQual))));

	foreach(l, qry->groupClause)
	{
		SortGroupClause *grpcl = (SortGroupClause *) lfirst(l);
		Node	   *expr;

		expr = get_sortgroupclause_expr(grpcl, qry->targetList);
		if (checkExprHasWindowFuncs(expr))
			ereport(ERROR,
					(errcode(ERRCODE_WINDOWING_ERROR),
				   errmsg("window functions not allowed in GROUP BY clause"),
					 parser_errposition(pstate,
										locate_windowfunc(expr))));
	}

	foreach(l, qry->windowClause)
	{
		WindowClause *wc = (WindowClause *) lfirst(l);
		ListCell   *l2;

		foreach(l2, wc->partitionClause)
		{
			SortGroupClause *grpcl = (SortGroupClause *) lfirst(l2);
			Node	   *expr;

			expr = get_sortgroupclause_expr(grpcl, qry->targetList);
			if (checkExprHasWindowFuncs(expr))
				ereport(ERROR,
						(errcode(ERRCODE_WINDOWING_ERROR),
				 errmsg("window functions not allowed in window definition"),
						 parser_errposition(pstate,
											locate_windowfunc(expr))));
		}
		foreach(l2, wc->orderClause)
		{
			SortGroupClause *grpcl = (SortGroupClause *) lfirst(l2);
			Node	   *expr;

			expr = get_sortgroupclause_expr(grpcl, qry->targetList);
			if (checkExprHasWindowFuncs(expr))
				ereport(ERROR,
						(errcode(ERRCODE_WINDOWING_ERROR),
				 errmsg("window functions not allowed in window definition"),
						 parser_errposition(pstate,
											locate_windowfunc(expr))));
		}
		/* startOffset and limitOffset were checked in transformFrameOffset */
	}
}

/*
 * check_ungrouped_columns -
 *	  Scan the given expression tree for ungrouped variables (variables
 *	  that are not listed in the groupClauses list and are not within
 *	  the arguments of aggregate functions).  Emit a suitable error message
 *	  if any are found.
 *
 * NOTE: we assume that the given clause has been transformed suitably for
 * parser output.  This means we can use expression_tree_walker.
 *
 * NOTE: we recognize grouping expressions in the main query, but only
 * grouping Vars in subqueries.  For example, this will be rejected,
 * although it could be allowed:
 *		SELECT
 *			(SELECT x FROM bar where y = (foo.a + foo.b))
 *		FROM foo
 *		GROUP BY a + b;
 * The difficulty is the need to account for different sublevels_up.
 * This appears to require a whole custom version of equal(), which is
 * way more pain than the feature seems worth.
 */
static void
check_ungrouped_columns(Node *node, ParseState *pstate, Query *qry,
						List *groupClauses, bool have_non_var_grouping,
						List **func_grouped_rels)
{
	check_ungrouped_columns_context context;

	context.pstate = pstate;
	context.qry = qry;
	context.groupClauses = groupClauses;
	context.have_non_var_grouping = have_non_var_grouping;
	context.func_grouped_rels = func_grouped_rels;
	context.sublevels_up = 0;
	check_ungrouped_columns_walker(node, &context);
}

static bool
check_ungrouped_columns_walker(Node *node,
							   check_ungrouped_columns_context *context)
{
	ListCell   *gl;

	if (node == NULL)
		return false;
	if (IsA(node, Const) ||
		IsA(node, Param))
		return false;			/* constants are always acceptable */

	/*
	 * If we find an aggregate call of the original level, do not recurse into
	 * its arguments; ungrouped vars in the arguments are not an error. We can
	 * also skip looking at the arguments of aggregates of higher levels,
	 * since they could not possibly contain Vars that are of concern to us
	 * (see transformAggregateCall).  We do need to look into the arguments of
	 * aggregates of lower levels, however.
	 */
	if (IsA(node, Aggref) &&
		(int) ((Aggref *) node)->agglevelsup >= context->sublevels_up)
		return false;

	/*
	 * If we have any GROUP BY items that are not simple Vars, check to see if
	 * subexpression as a whole matches any GROUP BY item. We need to do this
	 * at every recursion level so that we recognize GROUPed-BY expressions
	 * before reaching variables within them. But this only works at the outer
	 * query level, as noted above.
	 */
	if (context->have_non_var_grouping && context->sublevels_up == 0)
	{
		foreach(gl, context->groupClauses)
		{
			if (equal(node, lfirst(gl)))
				return false;	/* acceptable, do not descend more */
		}
	}

	/*
	 * If we have an ungrouped Var of the original query level, we have a
	 * failure.  Vars below the original query level are not a problem, and
	 * neither are Vars from above it.	(If such Vars are ungrouped as far as
	 * their own query level is concerned, that's someone else's problem...)
	 */
	if (IsA(node, Var))
	{
		Var		   *var = (Var *) node;
		RangeTblEntry *rte;
		char	   *attname;

		if (var->varlevelsup != context->sublevels_up)
			return false;		/* it's not local to my query, ignore */

		/*
		 * Check for a match, if we didn't do it above.
		 */
		if (!context->have_non_var_grouping || context->sublevels_up != 0)
		{
			foreach(gl, context->groupClauses)
			{
				Var		   *gvar = (Var *) lfirst(gl);

				if (IsA(gvar, Var) &&
					gvar->varno == var->varno &&
					gvar->varattno == var->varattno &&
					gvar->varlevelsup == 0)
					return false;		/* acceptable, we're okay */
			}
		}

		/*
		 * Check whether the Var is known functionally dependent on the GROUP
		 * BY columns.  If so, we can allow the Var to be used, because the
		 * grouping is really a no-op for this table.  However, this deduction
		 * depends on one or more constraints of the table, so we have to add
		 * those constraints to the query's constraintDeps list, because it's
		 * not semantically valid anymore if the constraint(s) get dropped.
		 * (Therefore, this check must be the last-ditch effort before raising
		 * error: we don't want to add dependencies unnecessarily.)
		 *
		 * Because this is a pretty expensive check, and will have the same
		 * outcome for all columns of a table, we remember which RTEs we've
		 * already proven functional dependency for in the func_grouped_rels
		 * list.  This test also prevents us from adding duplicate entries
		 * to the constraintDeps list.
		 */
		if (list_member_int(*context->func_grouped_rels, var->varno))
			return false;				/* previously proven acceptable */

		Assert(var->varno > 0 &&
			   (int) var->varno <= list_length(context->pstate->p_rtable));
		rte = rt_fetch(var->varno, context->pstate->p_rtable);
		if (rte->rtekind == RTE_RELATION)
		{
			if (check_functional_grouping(rte->relid,
										  var->varno,
										  0,
										  context->groupClauses,
										  &context->qry->constraintDeps))
			{
				*context->func_grouped_rels =
					lappend_int(*context->func_grouped_rels, var->varno);
				return false;			/* acceptable */
			}
		}

		/* Found an ungrouped local variable; generate error message */
		attname = get_rte_attribute_name(rte, var->varattno);
		if (context->sublevels_up == 0)
			ereport(ERROR,
					(errcode(ERRCODE_GROUPING_ERROR),
					 errmsg("column \"%s.%s\" must appear in the GROUP BY clause or be used in an aggregate function",
							rte->eref->aliasname, attname),
					 parser_errposition(context->pstate, var->location)));
		else
			ereport(ERROR,
					(errcode(ERRCODE_GROUPING_ERROR),
					 errmsg("subquery uses ungrouped column \"%s.%s\" from outer query",
							rte->eref->aliasname, attname),
					 parser_errposition(context->pstate, var->location)));
	}

	if (IsA(node, Query))
	{
		/* Recurse into subselects */
		bool		result;

		context->sublevels_up++;
		result = query_tree_walker((Query *) node,
								   check_ungrouped_columns_walker,
								   (void *) context,
								   0);
		context->sublevels_up--;
		return result;
	}
	return expression_tree_walker(node, check_ungrouped_columns_walker,
								  (void *) context);
}

/*
 * Create expression trees for the transition and final functions
 * of an aggregate.  These are needed so that polymorphic functions
 * can be used within an aggregate --- without the expression trees,
 * such functions would not know the datatypes they are supposed to use.
 * (The trees will never actually be executed, however, so we can skimp
 * a bit on correctness.)
 *
 * agg_input_types, agg_state_type, agg_result_type identify the input,
 * transition, and result types of the aggregate.  These should all be
 * resolved to actual types (ie, none should ever be ANYELEMENT etc).
 *
 * transfn_oid and finalfn_oid identify the funcs to be called; the latter
 * may be InvalidOid.
 *
 * Pointers to the constructed trees are returned into *transfnexpr and
 * *finalfnexpr.  The latter is set to NULL if there's no finalfn.
 */
void
build_aggregate_fnexprs(Oid *agg_input_types,
						int agg_num_inputs,
						Oid agg_state_type,
						Oid agg_result_type,
						Oid transfn_oid,
						Oid finalfn_oid,
						Expr **transfnexpr,
						Expr **finalfnexpr)
{
	Param	   *argp;
	List	   *args;
	int			i;

	/*
	 * Build arg list to use in the transfn FuncExpr node. We really only care
	 * that transfn can discover the actual argument types at runtime using
	 * get_fn_expr_argtype(), so it's okay to use Param nodes that don't
	 * correspond to any real Param.
	 */
	argp = makeNode(Param);
	argp->paramkind = PARAM_EXEC;
	argp->paramid = -1;
	argp->paramtype = agg_state_type;
	argp->paramtypmod = -1;
	argp->location = -1;

	args = list_make1(argp);

	for (i = 0; i < agg_num_inputs; i++)
	{
		argp = makeNode(Param);
		argp->paramkind = PARAM_EXEC;
		argp->paramid = -1;
		argp->paramtype = agg_input_types[i];
		argp->paramtypmod = -1;
		argp->location = -1;
		args = lappend(args, argp);
	}

	*transfnexpr = (Expr *) makeFuncExpr(transfn_oid,
										 agg_state_type,
										 args,
										 COERCE_DONTCARE);

	/* see if we have a final function */
	if (!OidIsValid(finalfn_oid))
	{
		*finalfnexpr = NULL;
		return;
	}

	/*
	 * Build expr tree for final function
	 */
	argp = makeNode(Param);
	argp->paramkind = PARAM_EXEC;
	argp->paramid = -1;
	argp->paramtype = agg_state_type;
	argp->paramtypmod = -1;
	argp->location = -1;
	args = list_make1(argp);

	*finalfnexpr = (Expr *) makeFuncExpr(finalfn_oid,
										 agg_result_type,
										 args,
										 COERCE_DONTCARE);
}