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 9b35253fe52d731d93700e9328b315592b441e72..46a4639eb50b4e5a0adee0bb45b0f616077e56f8 100644 (file)
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -2579,12 +2579,20 @@ 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;