Repair problem noted by Elphick: make_rels_by_joins failed to handle

cases where joinclauses were present but some joins have to be made
by cartesian-product join anyway.  An example is
SELECT * FROM a,b,c WHERE (a.f1 + b.f2 + c.f3) = 0;
Even though all the rels have joinclauses, we must join two of them
in cartesian style before we can use the join clause...

diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c
index 09003eb9fa852d5448b8ca94000cc0644a5a70aa..df37c58fc723493bedc992f9d69bd33785cfd97e 100644 (file)
--- a/src/backend/optimizer/path/joinrels.c
+++ b/src/backend/optimizer/path/joinrels.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinrels.c,v 1.44 2000/04/12 17:15:20 momjian Exp $
+ *   $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinrels.c,v 1.45 2000/04/27 18:35:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -39,6 +39,7 @@ static RelOptInfo *make_join_rel(Query *root, RelOptInfo *rel1,
 void
 make_rels_by_joins(Query *root, int level)
 {
+   List       *first_old_rel = root->join_rel_list;
    List       *r;
 
    /*
@@ -85,7 +86,9 @@ make_rels_by_joins(Query *root, int level)
             * Note that if all available join clauses for this rel
             * require more than one other rel, we will fail to make any
             * joins against it here.  That's OK; it'll be considered by
-            * "bushy plan" join code in a higher-level pass.
+            * "bushy plan" join code in a higher-level pass where we
+            * have those other rels collected into a join rel.  See also
+            * the last-ditch case below.
             */
            make_rels_by_clause_joins(root,
                                      old_rel,
@@ -161,6 +164,52 @@ make_rels_by_joins(Query *root, int level)
            }
        }
    }
+
+   /*
+    * Last-ditch effort: if we failed to find any usable joins so far,
+    * force a set of cartesian-product joins to be generated.  This
+    * handles the special case where all the available rels have join
+    * clauses but we cannot use any of the joins yet.  An example is
+    *
+    * SELECT * FROM a,b,c WHERE (a.f1 + b.f2 + c.f3) = 0;
+    *
+    * The join clause will be usable at level 3, but at level 2 we have
+    * no choice but to make cartesian joins.  We consider only left-sided
+    * and right-sided cartesian joins in this case (no bushy).
+    */
+   if (root->join_rel_list == first_old_rel)
+   {
+       /* This loop is just like the first one, except we always call
+        * make_rels_by_clauseless_joins().
+        */
+       if (level == 2)
+           r = root->base_rel_list; /* level-1 is base rels */
+       else
+           r = root->join_rel_list;
+       for (; r != NIL; r = lnext(r))
+       {
+           RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
+           int         old_level = length(old_rel->relids);
+           List       *other_rels;
+
+           if (old_level != level - 1)
+               break;
+
+           if (level == 2)
+               other_rels = lnext(r); /* only consider remaining base
+                                       * rels */
+           else
+               other_rels = root->base_rel_list; /* consider all base rels */
+
+           make_rels_by_clauseless_joins(root,
+                                         old_rel,
+                                         other_rels);
+       }
+
+       if (root->join_rel_list == first_old_rel)
+           elog(ERROR, "make_rels_by_joins: failed to build any %d-way joins",
+                level);
+   }
 }
 
 /*