Current implementation of FOR UPDATE has no hope of working correctly

for relations on the nullable side of an OUTER JOIN.  For now I think
we'd better refuse such queries.

diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index 5d67e02dacb44bce678665c592ab184f588469a5..c62fd5ecd7da51e48acc7ec89d54141b40c0d74b 100644 (file)
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $Header: /cvsroot/pgsql/src/backend/optimizer/plan/initsplan.c,v 1.60 2001/05/07 00:43:21 tgl Exp $
+ *   $Header: /cvsroot/pgsql/src/backend/optimizer/plan/initsplan.c,v 1.61 2001/05/14 20:25:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -298,7 +298,8 @@ mark_baserels_for_outer_join(Query *root, Relids rels, Relids outerrels)
 
    foreach(relid, rels)
    {
-       RelOptInfo *rel = get_base_rel(root, lfirsti(relid));
+       int         relno = lfirsti(relid);
+       RelOptInfo *rel = get_base_rel(root, relno);
 
        /*
         * Since we do this bottom-up, any outer-rels previously marked
@@ -306,6 +307,21 @@ mark_baserels_for_outer_join(Query *root, Relids rels, Relids outerrels)
         */
        Assert(is_subseti(rel->outerjoinset, outerrels));
 
+       /*
+        * Presently the executor cannot support FOR UPDATE marking of
+        * rels appearing on the nullable side of an outer join.
+        * (It's somewhat unclear what that would mean, anyway: what should
+        * we mark when a result row is generated from no element of the
+        * nullable relation?)  So, complain if target rel is FOR UPDATE.
+        * It's sufficient to make this check once per rel, so do it only
+        * if rel wasn't already known nullable.
+        */
+       if (rel->outerjoinset == NIL)
+       {
+           if (intMember(relno, root->rowMarks))
+               elog(ERROR, "SELECT FOR UPDATE cannot be applied to the nullable side of an OUTER JOIN");
+       }
+
        rel->outerjoinset = outerrels;
    }
 }