88 *
99 *
1010 * IDENTIFICATION
11- * $PostgreSQL: pgsql/src/backend/optimizer/path/joinpath.c,v 1.126 2009/09/19 17:48:09 tgl Exp $
11+ * $PostgreSQL: pgsql/src/backend/optimizer/path/joinpath.c,v 1.127 2009/12/25 17:11:32 tgl Exp $
1212 *
1313 *-------------------------------------------------------------------------
1414 */
@@ -228,6 +228,11 @@ join_is_removable(PlannerInfo *root,
228228 * We can't remove the join if any inner-rel attributes are used above
229229 * the join.
230230 *
231+ * Note that this test only detects use of inner-rel attributes in
232+ * higher join conditions and the target list. There might be such
233+ * attributes in pushed-down conditions at this join, too. We check
234+ * that case below.
235+ *
231236 * As a micro-optimization, it seems better to start with max_attr and
232237 * count down rather than starting with min_attr and counting up, on the
233238 * theory that the system attributes are somewhat less likely to be wanted
@@ -253,13 +258,16 @@ join_is_removable(PlannerInfo *root,
253258RestrictInfo * restrictinfo = (RestrictInfo * )lfirst (l );
254259
255260/*
256- * We are always considering an outer join here, so ignore pushed-down
257- * clauses. Also ignore anything that doesn't have a mergejoinable
258- * operator.
261+ * If we find a pushed-down clause, it must have come from above the
262+ * outer join and it must contain references to the inner rel. (If
263+ * it had only outer-rel variables, it'd have been pushed down into
264+ * the outer rel.) Therefore, we can conclude that join removal
265+ * is unsafe without any examination of the clause contents.
259266 */
260267if (restrictinfo -> is_pushed_down )
261- continue ;
268+ return false ;
262269
270+ /* Ignore if it's not a mergejoinable clause */
263271if (!restrictinfo -> can_join ||
264272restrictinfo -> mergeopfamilies == NIL )
265273continue ;/* not mergejoinable */