Teach planner to expand sufficiently simple SQL-language functions

('SELECT expression') inline, like macros, during the constant-folding
phase of planning.  The actual expansion is not difficult, but checking
that we're not changing the semantics of the call turns out to be more
subtle than one might think; in particular must pay attention to
permissions issues, strictness, and volatility.

src/backend/utils/cache/lsyscache.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/cache/lsyscache.c,v 1.86 2002/11/25 21:29:42 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/cache/lsyscache.c,v 1.87 2002/12/01 21:05:14 tgl Exp $
  *
  * NOTES
  *	  Eventually, the index information should go through here, too.
@@ -415,6 +415,22 @@ op_hashjoinable(Oid opno, Oid ltype, Oid rtype)
 	return result;
 }
 
+/*
+ * op_strict
+ *
+ * Get the proisstrict flag for the operator's underlying function.
+ */
+bool
+op_strict(Oid opno)
+{
+	RegProcedure funcid = get_opcode(opno);
+
+	if (funcid == (RegProcedure) InvalidOid)
+		elog(ERROR, "Operator OID %u does not exist", opno);
+
+	return func_strict((Oid) funcid);
+}
+
 /*
  * op_volatile
  *
@@ -606,6 +622,27 @@ get_func_retset(Oid funcid)
 	return result;
 }
 
+/*
+ * func_strict
+ *		Given procedure id, return the function's proisstrict flag.
+ */
+bool
+func_strict(Oid funcid)
+{
+	HeapTuple	tp;
+	bool		result;
+
+	tp = SearchSysCache(PROCOID,
+						ObjectIdGetDatum(funcid),
+						0, 0, 0);
+	if (!HeapTupleIsValid(tp))
+		elog(ERROR, "Function OID %u does not exist", funcid);
+
+	result = ((Form_pg_proc) GETSTRUCT(tp))->proisstrict;
+	ReleaseSysCache(tp);
+	return result;
+}
+
 /*
  * func_volatile
  *		Given procedure id, return the function's provolatile flag.

src/include/optimizer/clauses.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: clauses.h,v 1.55 2002/11/06 22:31:24 tgl Exp $
+ * $Id: clauses.h,v 1.56 2002/12/01 21:05:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -51,6 +51,7 @@ extern void check_subplans_for_ungrouped_vars(Query *query);
 
 extern bool contain_mutable_functions(Node *clause);
 extern bool contain_volatile_functions(Node *clause);
+extern bool contain_nonstrict_functions(Node *clause);
 
 extern bool is_pseudo_constant_clause(Node *clause);
 extern List *pull_constant_clauses(List *quals, List **constantQual);

src/include/utils/lsyscache.h

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: lsyscache.h,v 1.64 2002/09/19 23:40:56 tgl Exp $
+ * $Id: lsyscache.h,v 1.65 2002/12/01 21:05:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -31,6 +31,7 @@ extern bool op_mergejoinable(Oid opno, Oid ltype, Oid rtype,
 extern void op_mergejoin_crossops(Oid opno, Oid *ltop, Oid *gtop,
 					  RegProcedure *ltproc, RegProcedure *gtproc);
 extern Oid	op_hashjoinable(Oid opno, Oid ltype, Oid rtype);
+extern bool op_strict(Oid opno);
 extern char op_volatile(Oid opno);
 extern Oid	get_commutator(Oid opno);
 extern Oid	get_negator(Oid opno);
@@ -39,6 +40,7 @@ extern RegProcedure get_oprjoin(Oid opno);
 extern char *get_func_name(Oid funcid);
 extern Oid	get_func_rettype(Oid funcid);
 extern bool get_func_retset(Oid funcid);
+extern bool func_strict(Oid funcid);
 extern char func_volatile(Oid funcid);
 extern Oid	get_relname_relid(const char *relname, Oid relnamespace);
 extern Oid	get_system_catalog_relid(const char *catname);