Index: src/backend/optimizer/util/restrictinfo.c
===================================================================
RCS file: /home/hlinnaka/pgcvsrepository/pgsql/src/backend/optimizer/util/restrictinfo.c,v
retrieving revision 1.49
diff -c -r1.49 restrictinfo.c
*** src/backend/optimizer/util/restrictinfo.c	4 Oct 2006 00:29:55 -0000	1.49
--- src/backend/optimizer/util/restrictinfo.c	31 Jul 2007 08:58:40 -0000
***************
*** 651,656 ****
--- 651,659 ----
   * of the latter, even though they might seem redundant by the pathkey
   * membership test.
   *
+  * The above logic only works for normal join clauses with non-overlapping
+  * left and right relation sets.
+  *
   * Weird special case: if we have two clauses that seem redundant
   * except one is pushed down into an outer join and the other isn't,
   * then they're not really redundant, because one constrains the
***************
*** 673,685 ****
  			return refrinfo;
  	}

! 	/* check for redundant merge clauses */
! 	if (rinfo->mergejoinoperator != InvalidOid)
  	{
- 		/* do the cheap test first: is it a "var = const" clause? */
- 		if (bms_is_empty(rinfo->left_relids) ||
- 			bms_is_empty(rinfo->right_relids))
- 			return NULL;		/* var = const, so not redundant */

  		cache_mergeclause_pathkeys(root, rinfo);

--- 676,689 ----
  			return refrinfo;
  	}

! 	/*
! 	 * check for redundant merge clauses by comparing the pathkeys as 
! 	 * explained above. The check for can_join handles the special case
! 	 * of "var = const", as well as any clauses with overlapping left
! 	 * and right rel sets.
! 	 */
! 	if (rinfo->mergejoinoperator != InvalidOid && rinfo->can_join)
  	{

  		cache_mergeclause_pathkeys(root, rinfo);

***************
*** 687,693 ****
  		{
  			RestrictInfo *refrinfo = (RestrictInfo *) lfirst(refitem);

! 			if (refrinfo->mergejoinoperator != InvalidOid)
  			{
  				cache_mergeclause_pathkeys(root, refrinfo);

--- 691,697 ----
  		{
  			RestrictInfo *refrinfo = (RestrictInfo *) lfirst(refitem);

! 			if (refrinfo->mergejoinoperator != InvalidOid && refrinfo->can_join)
  			{
  				cache_mergeclause_pathkeys(root, refrinfo);