Fix inheritance count tracking in ALTER TABLE .. ADD CONSTRAINT.

Without this patch, constraints inherited by children of a parent
table which itself has multiple inheritance parents can end up with
the wrong coninhcount.  After dropping the constraint, the children
end up with a leftover copy of the constraint that is not dumped
and cannot be dropped.  There is a similar problem with ALTER TABLE
.. ADD COLUMN, but that looks significantly more difficult to
resolve, so I'm committing this fix separately.

Back-patch to 8.4, which is the first release that has coninhcount.

Report by Hank Enting.

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index ff27b73..4c79f8f 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.332.2.2 2010/07/29 19:23:28 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.332.2.3 2010/08/03 15:47:09 rhaas Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -4703,6 +4703,15 @@ ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
        CommandCounterIncrement();
 
        /*
+        * If the constraint got merged with an existing constraint, we're done.
+        * We mustn't recurse to child tables in this case, because they've already
+        * got the constraint, and visiting them again would lead to an incorrect
+        * value for coninhcount.
+        */
+       if (newcons == NIL)
+               return;
+
+       /*
         * Propagate to children as appropriate.  Unlike most other ALTER
         * routines, we have to do this one level of recursion at a time; we can't
         * use find_all_inheritors to do it in one pass.