Arrange to "inline" SQL functions that appear in a query's FROM clause,

are declared to return set, and consist of just a single SELECT.  We
can replace the FROM-item with a sub-SELECT and then optimize much as
if we were dealing with a view.  Patch from Richard Rowell, cleaned up
by me.

src/backend/catalog/pg_proc.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/catalog/pg_proc.c,v 1.148 2008/01/01 19:45:48 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/catalog/pg_proc.c,v 1.149 2008/03/18 22:04:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -601,7 +601,8 @@ fmgr_sql_validator(PG_FUNCTION_ARGS)
 												  proc->proargtypes.values,
 												  proc->pronargs);
 			(void) check_sql_fn_retval(funcoid, proc->prorettype,
-									   querytree_list, NULL);
+									   querytree_list,
+									   false, NULL);
 		}
 		else
 			querytree_list = pg_parse_query(prosrc);

src/backend/executor/functions.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/functions.c,v 1.120 2008/01/01 19:45:49 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/functions.c,v 1.121 2008/03/18 22:04:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -20,6 +20,7 @@
 #include "commands/trigger.h"
 #include "executor/functions.h"
 #include "funcapi.h"
+#include "nodes/makefuncs.h"
 #include "parser/parse_coerce.h"
 #include "parser/parse_expr.h"
 #include "tcop/tcopprot.h"
@@ -269,6 +270,7 @@ init_sql_fcache(FmgrInfo *finfo)
 	fcache->returnsTuple = check_sql_fn_retval(foid,
 											   rettype,
 											   queryTree_list,
+											   false,
 											   &fcache->junkFilter);
 
 	/* Finally, plan the queries */
@@ -856,7 +858,9 @@ ShutdownSQLFunction(Datum arg)
  *
  * The return value of a sql function is the value returned by
  * the final query in the function.  We do some ad-hoc type checking here
- * to be sure that the user is returning the type he claims.
+ * to be sure that the user is returning the type he claims.  There are
+ * also a couple of strange-looking features to assist callers in dealing
+ * with allowed special cases, such as binary-compatible result types.
  *
  * For a polymorphic function the passed rettype must be the actual resolved
  * output type of the function; we should never see a polymorphic pseudotype
@@ -868,6 +872,10 @@ ShutdownSQLFunction(Datum arg)
  * allow "SELECT rowtype_expression", this may be false even when the declared
  * function return type is a rowtype.
  *
+ * If insertRelabels is true, then binary-compatible cases are dealt with
+ * by actually inserting RelabelType nodes into the final SELECT; obviously
+ * the caller must pass a parsetree that it's okay to modify in this case.
+ *
  * If junkFilter isn't NULL, then *junkFilter is set to a JunkFilter defined
  * to convert the function's tuple result to the correct output tuple type.
  * Whenever the result value is false (ie, the function isn't returning a
@@ -875,6 +883,7 @@ ShutdownSQLFunction(Datum arg)
  */
 bool
 check_sql_fn_retval(Oid func_id, Oid rettype, List *queryTreeList,
+					bool insertRelabels,
 					JunkFilter **junkFilter)
 {
 	Query	   *parse;
@@ -945,10 +954,12 @@ check_sql_fn_retval(Oid func_id, Oid rettype, List *queryTreeList,
 		rettype == VOIDOID)
 	{
 		/*
-		 * For scalar-type returns, the target list should have exactly one
-		 * entry, and its type should agree with what the user declared. (As
-		 * of Postgres 7.2, we accept binary-compatible types too.)
+		 * For scalar-type returns, the target list must have exactly one
+		 * non-junk entry, and its type must agree with what the user
+		 * declared; except we allow binary-compatible types too.
 		 */
+		TargetEntry *tle;
+
 		if (tlistlen != 1)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
@@ -956,7 +967,11 @@ check_sql_fn_retval(Oid func_id, Oid rettype, List *queryTreeList,
 					format_type_be(rettype)),
 				 errdetail("Final SELECT must return exactly one column.")));
 
-		restype = exprType((Node *) ((TargetEntry *) linitial(tlist))->expr);
+		/* We assume here that non-junk TLEs must come first in tlists */
+		tle = (TargetEntry *) linitial(tlist);
+		Assert(!tle->resjunk);
+
+		restype = exprType((Node *) tle->expr);
 		if (!IsBinaryCoercible(restype, rettype))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
@@ -964,6 +979,11 @@ check_sql_fn_retval(Oid func_id, Oid rettype, List *queryTreeList,
 					format_type_be(rettype)),
 					 errdetail("Actual return type is %s.",
 							   format_type_be(restype))));
+		if (insertRelabels && restype != rettype)
+			tle->expr = (Expr *) makeRelabelType(tle->expr,
+												 rettype,
+												 -1,
+												 COERCE_DONTCARE);
 	}
 	else if (fn_typtype == TYPTYPE_COMPOSITE || rettype == RECORDOID)
 	{
@@ -977,15 +997,25 @@ check_sql_fn_retval(Oid func_id, Oid rettype, List *queryTreeList,
 		 * If the target list is of length 1, and the type of the varnode in
 		 * the target list matches the declared return type, this is okay.
 		 * This can happen, for example, where the body of the function is
-		 * 'SELECT func2()', where func2 has the same return type as the
-		 * function that's calling it.
+		 * 'SELECT func2()', where func2 has the same composite return type
+		 * as the function that's calling it.
 		 */
 		if (tlistlen == 1)
 		{
-			restype = exprType((Node *) ((TargetEntry *) linitial(tlist))->expr);
+			TargetEntry *tle = (TargetEntry *) linitial(tlist);
+
+			Assert(!tle->resjunk);
+			restype = exprType((Node *) tle->expr);
 			if (IsBinaryCoercible(restype, rettype))
+			{
+				if (insertRelabels && restype != rettype)
+					tle->expr = (Expr *) makeRelabelType(tle->expr,
+														 rettype,
+														 -1,
+														 COERCE_DONTCARE);
 				return false;	/* NOT returning whole tuple */
 			}
+		}
 
 		/* Is the rowtype fixed, or determined only at runtime? */
 		if (get_func_result_type(func_id, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
@@ -1043,6 +1073,11 @@ check_sql_fn_retval(Oid func_id, Oid rettype, List *queryTreeList,
 								   format_type_be(tletype),
 								   format_type_be(atttype),
 								   tuplogcols)));
+			if (insertRelabels && tletype != atttype)
+				tle->expr = (Expr *) makeRelabelType(tle->expr,
+													 atttype,
+													 -1,
+													 COERCE_DONTCARE);
 		}
 
 		for (;;)
@@ -1070,14 +1105,6 @@ check_sql_fn_retval(Oid func_id, Oid rettype, List *queryTreeList,
 		/* Report that we are returning entire tuple result */
 		return true;
 	}
-	else if (IsPolymorphicType(rettype))
-	{
-		/* This should already have been caught ... */
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
-				 errmsg("cannot determine result data type"),
-				 errdetail("A function returning a polymorphic type must have at least one polymorphic argument.")));
-	}
 	else
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),

src/backend/optimizer/plan/planner.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.226 2008/01/01 19:45:50 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.227 2008/03/18 22:04:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -253,13 +253,20 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 	/*
 	 * Look for IN clauses at the top level of WHERE, and transform them into
 	 * joins.  Note that this step only handles IN clauses originally at top
-	 * level of WHERE; if we pull up any subqueries in the next step, their
-	 * INs are processed just before pulling them up.
+	 * level of WHERE; if we pull up any subqueries below, their INs are
+	 * processed just before pulling them up.
 	 */
 	if (parse->hasSubLinks)
 		parse->jointree->quals = pull_up_IN_clauses(root,
 													parse->jointree->quals);
 
+	/*
+	 * Scan the rangetable for set-returning functions, and inline them
+	 * if possible (producing subqueries that might get pulled up next).
+	 * Recursion issues here are handled in the same way as for IN clauses.
+	 */
+	inline_set_returning_functions(root);
+
 	/*
 	 * Check to see if any subqueries in the rangetable can be merged into
 	 * this query.

src/backend/optimizer/prep/prepjointree.c

@@ -5,6 +5,7 @@
  *
  * NOTE: the intended sequence for invoking these operations is
  *		pull_up_IN_clauses
+ *		inline_set_returning_functions
  *		pull_up_subqueries
  *		do expression preprocessing (including flattening JOIN alias vars)
  *		reduce_outer_joins
@@ -15,7 +16,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.49 2008/01/01 19:45:50 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.50 2008/03/18 22:04:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -124,6 +125,52 @@ pull_up_IN_clauses(PlannerInfo *root, Node *node)
 	return node;
 }
 
+/*
+ * inline_set_returning_functions
+ *		Attempt to "inline" set-returning functions in the FROM clause.
+ *
+ * If an RTE_FUNCTION rtable entry invokes a set-returning function that
+ * contains just a simple SELECT, we can convert the rtable entry to an
+ * RTE_SUBQUERY entry exposing the SELECT directly.  This is especially
+ * useful if the subquery can then be "pulled up" for further optimization,
+ * but we do it even if not, to reduce executor overhead.
+ *
+ * This has to be done before we have started to do any optimization of
+ * subqueries, else any such steps wouldn't get applied to subqueries
+ * obtained via inlining.  However, we do it after pull_up_IN_clauses
+ * so that we can inline any functions used in IN subselects.
+ *
+ * Like most of the planner, this feels free to scribble on its input data
+ * structure.
+ */
+void
+inline_set_returning_functions(PlannerInfo *root)
+{
+	ListCell   *rt;
+
+	foreach(rt, root->parse->rtable)
+	{
+		RangeTblEntry *rte = (RangeTblEntry *) lfirst(rt);
+
+		if (rte->rtekind == RTE_FUNCTION)
+		{
+			Query  *funcquery;
+
+			/* Check safety of expansion, and expand if possible */
+			funcquery = inline_set_returning_function(root, rte->funcexpr);
+			if (funcquery)
+			{
+				/* Successful expansion, replace the rtable entry */
+				rte->rtekind = RTE_SUBQUERY;
+				rte->subquery = funcquery;
+				rte->funcexpr = NULL;
+				rte->funccoltypes = NIL;
+				rte->funccoltypmods = NIL;
+			}
+		}
+	}
+}
+
 /*
  * pull_up_subqueries
  *		Look for subqueries in the rangetable that can be pulled up into
@@ -296,6 +343,7 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 	subroot->query_level = root->query_level;
 	subroot->planner_cxt = CurrentMemoryContext;
 	subroot->init_plans = NIL;
+	subroot->eq_classes = NIL;
 	subroot->in_info_list = NIL;
 	subroot->append_rel_list = NIL;
 
@@ -307,6 +355,11 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 		subquery->jointree->quals = pull_up_IN_clauses(subroot,
 												  subquery->jointree->quals);
 
+	/*
+	 * Similarly, inline any set-returning functions in its rangetable.
+	 */
+	inline_set_returning_functions(subroot);
+
 	/*
 	 * Recursively pull up the subquery's subqueries, so that
 	 * pull_up_subqueries' processing is complete for its jointree and

src/include/executor/functions.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/executor/functions.h,v 1.30 2008/01/01 19:45:57 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/executor/functions.h,v 1.31 2008/03/18 22:04:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -21,6 +21,7 @@ extern Datum fmgr_sql(PG_FUNCTION_ARGS);
 
 extern bool check_sql_fn_retval(Oid func_id, Oid rettype,
 					List *queryTreeList,
+					bool insertRelabels,
 					JunkFilter **junkFilter);
 
 #endif   /* FUNCTIONS_H */

src/include/optimizer/clauses.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/clauses.h,v 1.88 2008/01/01 19:45:58 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/clauses.h,v 1.89 2008/03/18 22:04:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -79,6 +79,8 @@ extern Node *eval_const_expressions(Node *node);
 
 extern Node *estimate_expression_value(PlannerInfo *root, Node *node);
 
+extern Query *inline_set_returning_function(PlannerInfo *root, Node *node);
+
 extern bool expression_tree_walker(Node *node, bool (*walker) (),
 											   void *context);
 extern Node *expression_tree_mutator(Node *node, Node *(*mutator) (),

src/include/optimizer/prep.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/prep.h,v 1.59 2008/01/01 19:45:58 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/prep.h,v 1.60 2008/03/18 22:04:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -22,6 +22,7 @@
  * prototypes for prepjointree.c
  */
 extern Node *pull_up_IN_clauses(PlannerInfo *root, Node *node);
+extern void inline_set_returning_functions(PlannerInfo *root);
 extern Node *pull_up_subqueries(PlannerInfo *root, Node *jtnode,
 				   bool below_outer_join, bool append_rel_member);
 extern void reduce_outer_joins(PlannerInfo *root);