Modify planner's implied-equality-deduction code so that when a set

of known-equal expressions includes any constant expressions (including
Params from outer queries), we actively suppress any 'var = var'
clauses that are or could be deduced from the set, generating only the
deducible 'var = const' clauses instead.  The idea here is to push down
the restrictions implied by the equality set to base relations whenever
possible.  Once we have applied the 'var = const' clauses, the 'var = var'
clauses are redundant, and should be suppressed both to save work at
execution and to avoid double-counting restrictivity.

src/backend/nodes/list.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/nodes/list.c,v 1.44 2003/01/20 18:54:47 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/nodes/list.c,v 1.45 2003/01/24 03:58:34 tgl Exp $
  *
  * NOTES
  *	  XXX a few of the following functions are duplicated to handle
@@ -357,6 +357,7 @@ set_union(List *l1, List *l2)
 	return retval;
 }
 
+/* set_union for integer lists */
 List *
 set_unioni(List *l1, List *l2)
 {
@@ -371,6 +372,21 @@ set_unioni(List *l1, List *l2)
 	return retval;
 }
 
+/* set_union when pointer-equality comparison is sufficient */
+List *
+set_ptrUnion(List *l1, List *l2)
+{
+	List	   *retval = listCopy(l1);
+	List	   *i;
+
+	foreach(i, l2)
+	{
+		if (!ptrMember(lfirst(i), retval))
+			retval = lappend(retval, lfirst(i));
+	}
+	return retval;
+}
+
 /*
  * Generate the intersection of two lists,
  * ie, all members of both l1 and l2.