Fix adjust_semi_join to be more cautious about clauseless joins.

tglsfdc · tglsfdc · commit 3f36070d72a5 · 2010-11-02T18:45:44.000-04:00
It was reporting that these were fully indexed (hence cheap), when of
course they're the exact opposite of that.  I'm not certain if the case
would arise in practice, since a clauseless semijoin is hard to produce
in SQL, but if it did happen we'd make some dumb decisions.
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
@@ -2810,12 +2810,20 @@ adjust_semi_join(PlannerInfo *root, JoinPath *path, SpecialJoinInfo *sjinfo,
 	 */
 	if (indexed_join_quals)
 	{
-		List	   *nrclauses;
+		if (path->joinrestrictinfo != NIL)
+		{
+			List	   *nrclauses;
 
-		nrclauses = select_nonredundant_join_clauses(root,
-													 path->joinrestrictinfo,
-													 path->innerjoinpath);
-		*indexed_join_quals = (nrclauses == NIL);
+			nrclauses = select_nonredundant_join_clauses(root,
+														 path->joinrestrictinfo,
+														 path->innerjoinpath);
+			*indexed_join_quals = (nrclauses == NIL);
+		}
+		else
+		{
+			/* a clauseless join does NOT qualify */
+			*indexed_join_quals = false;
+		}
 	}
 
 	return true;
