MWL#89: Cost-based choice between Materialization and IN->EXISTS transformation

Fixes for multiple problems/bugs/test failures that resulted from moving
subquery optimization from the execution phase to the optimization phase.

1 files changed, 14 insertions, 0 deletions

diff --git a/sql/sql_union.cc b/sql/sql_union.cc
index 374e92c6a52..d91bdc069e8 100644
--- a/sql/sql_union.cc
+++ b/sql/sql_union.cc
@@ -186,6 +186,8 @@ st_select_lex_unit::init_prepare_fake_select_lex(THD *thd_arg)
   {
     (*order->item)->walk(&Item::change_context_processor, 0,
                          (uchar*) &fake_select_lex->context);
+    (*order->item)->walk(&Item::set_fake_select_as_master_processor, 0,
+                         (uchar*) fake_select_lex);
   }
 }
 
@@ -271,6 +273,18 @@ bool st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
 
     can_skip_order_by= is_union_select && !(sl->braces && sl->explicit_limit);
 
+    /*
+      Remove all references from the select_lex_units to the subqueries that
+      are inside the ORDER BY clause.
+    */
+    if (can_skip_order_by)
+    {
+      for (ORDER *ord= (ORDER *)sl->order_list.first; ord; ord= ord->next)
+      {
+        (*ord->item)->walk(&Item::eliminate_subselect_processor, FALSE, NULL);
+      }
+    }
+
     saved_error= join->prepare(&sl->ref_pointer_array,
                                (TABLE_LIST*) sl->table_list.first,
                                sl->with_wild,