pull_up_subqueries() should copy the subquery before starting to modify

it.  Not sure why I'd thought it would be a good idea to do differently
way back when, but Greg Stark exposed the folly of doing so ...

diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index 687a702c78805f6dfbdbedaef4d565fa69823bb3..0597573213364f99c751607306262c2103ea7872 100644 (file)
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -16,7 +16,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.12 2003/09/25 06:58:00 petere Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.13 2003/10/13 23:48:16 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -148,9 +148,10 @@ pull_up_subqueries(Query *parse, Node *jtnode, bool below_outer_join)
                 * If we are inside an outer join, only pull up subqueries whose
                 * targetlists are nullable --- otherwise substituting their tlist
                 * entries for upper Var references would do the wrong thing (the
-                * results wouldn't become NULL when they're supposed to). XXX
-                * This could be improved by generating pseudo-variables for such
-                * expressions; we'd have to figure out how to get the pseudo-
+                * results wouldn't become NULL when they're supposed to).
+                *
+                * XXX This could be improved by generating pseudo-variables for
+                * such expressions; we'd have to figure out how to get the pseudo-
                 * variables evaluated at the right place in the modified plan
                 * tree. Fix it someday.
                 *
@@ -167,7 +168,15 @@ pull_up_subqueries(Query *parse, Node *jtnode, bool below_outer_join)
                        List       *rt;
 
                        /*
-                        * First, pull up any IN clauses within the subquery's WHERE,
+                        * First make a modifiable copy of the subquery.  This avoids
+                        * problems if the same subquery is referenced from multiple
+                        * jointree items (which can't happen normally, but might after
+                        * rule rewriting).
+                        */
+                       subquery = copyObject(subquery);
+
+                       /*
+                        * Pull up any IN clauses within the subquery's WHERE,
                         * so that we don't leave unoptimized INs behind.
                         */
                        if (subquery->hasSubLinks)
@@ -175,15 +184,9 @@ pull_up_subqueries(Query *parse, Node *jtnode, bool below_outer_join)
                                                                                          subquery->jointree->quals);
 
                        /*
-                        * Now, recursively pull up the subquery's subqueries, so that
+                        * Recursively pull up the subquery's subqueries, so that
                         * this routine's processing is complete for its jointree and
-                        * rangetable.  NB: if the same subquery is referenced from
-                        * multiple jointree items (which can't happen normally, but
-                        * might after rule rewriting), then we will invoke this
-                        * processing multiple times on that subquery.  OK because
-                        * nothing will happen after the first time.  We do have to be
-                        * careful to copy everything we pull up, however, or risk
-                        * having chunks of structure multiply linked.
+                        * rangetable.
                         *
                         * Note: 'false' is correct here even if we are within an outer
                         * join in the upper query; the lower query starts with a
@@ -193,12 +196,6 @@ pull_up_subqueries(Query *parse, Node *jtnode, bool below_outer_join)
                                pull_up_subqueries(subquery, (Node *) subquery->jointree,
                                                                   false);
 
-                       /*
-                        * Now make a modifiable copy of the subquery that we can run
-                        * OffsetVarNodes and IncrementVarSublevelsUp on.
-                        */
-                       subquery = copyObject(subquery);
-
                        /*
                         * Adjust level-0 varnos in subquery so that we can append its
                         * rangetable to upper query's.