Add COST and ROWS options to CREATE/ALTER FUNCTION, plus underlying pg_proc

columns procost and prorows, to allow simple user adjustment of the estimated
cost of a function call, as well as control of the estimated number of rows
returned by a set-returning function.  We might eventually wish to extend this
to allow function-specific estimation routines, but there seems to be
consensus that we should try a simple constant estimate first.  In particular
this provides a relatively simple way to control the order in which different
WHERE clauses are applied in a plan node, which is a Good Thing in view of the
fact that the recent EquivalenceClass planner rewrite made that much less
predictable than before.

src/backend/parser/keywords.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/keywords.c,v 1.181 2007/01/09 02:14:14 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/keywords.c,v 1.182 2007/01/22 01:35:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -93,6 +93,7 @@ static const ScanKeyword ScanKeywords[] = {
 	{"conversion", CONVERSION_P},
 	{"convert", CONVERT},
 	{"copy", COPY},
+	{"cost", COST},
 	{"create", CREATE},
 	{"createdb", CREATEDB},
 	{"createrole", CREATEROLE},