Make eval_const_expressions simplify FieldSelect from a whole-row Var

into an ordinary one-field Var.  Per example from Chris Mungall.

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index fcd583741893133c4b7b5cf31c15d749b6581761..bdad4d9b811f91b866a10a5c3d4e0c75e943dc01 100644 (file)
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.131 2003/03/10 03:53:50 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.132 2003/03/14 00:55:17 tgl Exp $
  *
  * HISTORY
  *       AUTHOR                        DATE                    MAJOR EVENT
@@ -1497,6 +1497,28 @@ eval_const_expressions_mutator(Node *node, List *active_fns)
                newcoalesce->args = newargs;
                return (Node *) newcoalesce;
        }
+       if (IsA(node, FieldSelect))
+       {
+               /*
+                * We can optimize field selection from a whole-row Var into a
+                * simple Var.  (This case won't be generated directly by the
+                * parser, because ParseComplexProjection short-circuits it.
+                * But it can arise while simplifying functions.)  If the argument
+                * isn't a whole-row Var, just fall through to do generic processing.
+                */
+               FieldSelect *fselect = (FieldSelect *) node;
+               Var                *argvar = (Var *) fselect->arg;
+
+               if (argvar && IsA(argvar, Var) &&
+                       argvar->varattno == InvalidAttrNumber)
+               {
+                       return (Node *) makeVar(argvar->varno,
+                                                                       fselect->fieldnum,
+                                                                       fselect->resulttype,
+                                                                       fselect->resulttypmod,
+                                                                       argvar->varlevelsup);
+               }
+       }
 
        /*
         * For any node type not handled above, we recurse using