fixed support of used_tables() and const_item() in subqueries

(BUG#1444)

1 files changed, 45 insertions, 3 deletions

diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
index 5e0221ad6c7..4ad49ebec74 100644
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@@ -36,7 +36,8 @@ inline Item * and_items(Item* cond, Item *item)
 
 Item_subselect::Item_subselect():
   Item_result_field(), engine_owner(1), value_assigned(0), substitution(0),
-  engine(0), have_to_be_excluded(0), engine_changed(0)
+  engine(0), used_tables_cache(0), have_to_be_excluded(0),
+  const_item_cache(1), engine_changed(0)
 {
   reset();
   /*
@@ -146,12 +147,27 @@ void Item_subselect::fix_length_and_dec()
   engine->fix_length_and_dec(0);
 }
 
-inline table_map Item_subselect::used_tables() const
+table_map Item_subselect::used_tables() const
 {
-  return (table_map) (engine->dependent() ? 1L :
+  return (table_map) (engine->dependent() ? used_tables_cache :
 		      (engine->uncacheable() ? RAND_TABLE_BIT : 0L));
 }
 
+bool Item_subselect::const_item() const
+{
+  return engine->uncacheable()? 0 : const_item_cache;
+}
+
+void Item_subselect::update_used_tables()
+{
+  if (!engine->uncacheable())
+  {
+    // did all used tables become ststic?
+    if ((used_tables_cache & ~engine->upper_select_const_tables()) == 0)
+      const_item_cache= 1;
+  }
+}
+
 Item_singlerow_subselect::Item_singlerow_subselect(st_select_lex *select_lex)
   :Item_subselect(), value(0)
 {
@@ -1138,3 +1154,29 @@ void subselect_uniquesubquery_engine::exclude()
   //this never should be called
   DBUG_ASSERT(0);
 }
+
+
+table_map subselect_engine::calc_const_tables(TABLE_LIST *table)
+{
+  table_map map= 0;
+  for(; table; table= table->next)
+  {
+    TABLE *tbl= table->table;
+    if (tbl && tbl->const_table)
+      map|= tbl->map;
+  }
+  return map;
+}
+
+
+table_map subselect_single_select_engine::upper_select_const_tables()
+{
+  return calc_const_tables((TABLE_LIST *) select_lex->outer_select()->
+			   table_list.first);
+}
+
+table_map subselect_union_engine::upper_select_const_tables()
+{
+  return calc_const_tables((TABLE_LIST *) unit->outer_select()->
+			   table_list.first);
+}