Merge olga.mysql.com:/home/igor/mysql-4.1-opt

into  olga.mysql.com:/home/igor/mysql-5.0-opt


sql/item_subselect.cc:
  Auto merged
mysql-test/r/subselect.result:
  Manual merge
mysql-test/t/subselect.test:
  Manual merge
sql/item_subselect.h:
  Manual merge

2 files changed, 19 insertions, 3 deletions

diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
index bffecb3c84c..4910fff4c4e 100644
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@@ -349,6 +349,7 @@ Item_singlerow_subselect::select_transformer(JOIN *join)
       */
       !(select_lex->item_list.head()->type() == FIELD_ITEM ||
 	select_lex->item_list.head()->type() == REF_ITEM) &&
+      !join->conds && !join->having &&
       /*
         switch off this optimization for prepare statement,
         because we do not rollback this changes
@@ -373,8 +374,6 @@ Item_singlerow_subselect::select_transformer(JOIN *join)
     */
     substitution->walk(&Item::remove_dependence_processor,
 		       (byte *) select_lex->outer_select());
-    /* SELECT without FROM clause can't have WHERE or HAVING clause */
-    DBUG_ASSERT(join->conds == 0 && join->having == 0);
     return RES_REDUCE;
   }
   return RES_OK;
@@ -2278,6 +2277,22 @@ bool subselect_single_select_engine::no_tables()
 
 
 /*
+  Check statically whether the subquery can return NULL
+
+  SINOPSYS
+    subselect_single_select_engine::may_be_null()
+
+  RETURN
+    FALSE  can guarantee that the subquery never return NULL
+    TRUE   otherwise
+*/
+bool subselect_single_select_engine::may_be_null()
+{
+  return ((no_tables() && !join->conds && !join->having) ? maybe_null : 1);
+}
+
+
+/*
   Report about presence of tables in subquery
 
   SYNOPSIS
diff --git a/sql/item_subselect.h b/sql/item_subselect.h
index 35ded79b75d..e9edb157f54 100644
--- a/sql/item_subselect.h
+++ b/sql/item_subselect.h
@@ -363,7 +363,7 @@ public:
   enum Item_result type() { return res_type; }
   enum_field_types field_type() { return res_field_type; }
   virtual void exclude()= 0;
-  bool may_be_null() { return maybe_null; };
+  virtual bool may_be_null() { return maybe_null; };
   virtual table_map upper_select_const_tables()= 0;
   static table_map calc_const_tables(TABLE_LIST *);
   virtual void print(String *str)= 0;
@@ -400,6 +400,7 @@ public:
   void print (String *str);
   bool change_result(Item_subselect *si, select_subselect *result);
   bool no_tables();
+  bool may_be_null();
   bool is_executed() const { return executed; }
   bool no_rows();
 };