Ensure that mergejoin plan will be considered for FULL OUTER JOIN even

if enable_mergejoin = OFF.  Must do this, because we have no other
implementation method for full joins.

src/backend/optimizer/path/joinpath.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinpath.c,v 1.58 2000/10/05 19:48:26 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinpath.c,v 1.59 2000/11/23 03:57:31 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -75,9 +75,12 @@ add_paths_to_joinrel(Query *root,
 	List	   *mergeclause_list = NIL;
 
 	/*
-	 * Find potential mergejoin clauses.
+	 * Find potential mergejoin clauses.  We can skip this if we are not
+	 * interested in doing a mergejoin.  However, mergejoin is currently
+	 * our only way of implementing full outer joins, so override
+	 * mergejoin disable if it's a full join.
 	 */
-	if (enable_mergejoin)
+	if (enable_mergejoin || jointype == JOIN_FULL)
 		mergeclause_list = select_mergejoin_clauses(joinrel,
 													outerrel,
 													innerrel,

src/backend/optimizer/plan/initsplan.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/initsplan.c,v 1.52 2000/11/16 22:30:25 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/initsplan.c,v 1.53 2000/11/23 03:57:31 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -454,9 +454,13 @@ distribute_qual_to_rels(Query *root, Node *clause,
 		 * joining.
 		 *
 		 * We don't bother setting the merge/hashjoin info if we're not
-		 * going to need it.
+		 * going to need it.  We do want to know about mergejoinable ops
+		 * in any potential equijoin clause (see later in this routine),
+		 * and we ignore enable_mergejoin if isouterjoin is true, because
+		 * mergejoin is the only implementation we have for full and right
+		 * outer joins.
 		 */
-		if (enable_mergejoin || can_be_equijoin)
+		if (enable_mergejoin || isouterjoin || can_be_equijoin)
 			check_mergejoinable(restrictinfo);
 		if (enable_hashjoin)
 			check_hashjoinable(restrictinfo);