Index: joinrels.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/optimizer/path/joinrels.c,v
retrieving revision 1.100.2.1
diff -c -r1.100.2.1 joinrels.c
*** joinrels.c	19 Jul 2009 20:32:56 -0000	1.100.2.1
--- joinrels.c	23 Jul 2009 17:39:13 -0000
***************
*** 400,405 ****
--- 400,421 ----
  			continue;
  
  		/*
+ 		 * If it's a semijoin and we already joined the RHS to any other
+ 		 * rels within either input, then we must have unique-ified the RHS
+ 		 * at that point (see below).  Therefore the semijoin is no longer
+ 		 * relevant in this join path.
+ 		 */
+ 		if (sjinfo->jointype == JOIN_SEMI)
+ 		{
+ 			if (bms_is_subset(sjinfo->syn_righthand, rel1->relids) &&
+ 				!bms_equal(sjinfo->syn_righthand, rel1->relids))
+ 				continue;
+ 			if (bms_is_subset(sjinfo->syn_righthand, rel2->relids) &&
+ 				!bms_equal(sjinfo->syn_righthand, rel2->relids))
+ 				continue;
+ 		}
+ 
+ 		/*
  		 * If one input contains min_lefthand and the other contains
  		 * min_righthand, then we can perform the SJ at this join.
  		 *
***************
*** 491,499 ****
  			 * We assume that make_outerjoininfo() set things up correctly
  			 * so that we'll only match to some SJ if the join is valid.
  			 * Set flag here to check at bottom of loop.
- 			 *
- 			 * For a semijoin, assume it's okay if either side fully contains
- 			 * the RHS (per the unique-ification case above).
  			 *----------
  			 */
  			if (sjinfo->jointype != JOIN_SEMI &&
--- 507,512 ----
***************
*** 503,514 ****
  				/* seems OK */
  				Assert(!bms_overlap(joinrelids, sjinfo->min_lefthand));
  			}
- 			else if (sjinfo->jointype == JOIN_SEMI &&
- 					 (bms_is_subset(sjinfo->syn_righthand, rel1->relids) ||
- 					  bms_is_subset(sjinfo->syn_righthand, rel2->relids)))
- 			{
- 				/* seems OK */
- 			}
  			else
  				is_valid_inner = false;
  		}
--- 516,521 ----