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 6f16eb81dcd30eaa11b0c709d66ef68761a2550a..b27c26154cc8d908e459579af144df8affd9b33c 100644 (file)
--- 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;