Fix adjust_semi_join to be more cautious about clauseless joins.

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
index 067cbca1254d7b58114edf40e7c9ec967ce86f88..16a5d0a3ca277a8ad4d735eb43940bc6f46560f7 100644 (file)
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -2897,12 +2897,20 @@ 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;