implement Item_singlerow_subselect::get_date() to avoid

unnecessary date->string->date conversion

sql/item_subselect.cc

@@ -1178,6 +1178,24 @@ bool Item_singlerow_subselect::val_bool()
 }
 
 
+bool Item_singlerow_subselect::get_date(MYSQL_TIME *ltime,uint fuzzydate)
+{
+  DBUG_ASSERT(fixed == 1);
+  if (forced_const)
+    return value->get_date(ltime, fuzzydate);
+  if (!exec() && !value->null_value)
+  {
+    null_value= FALSE;
+    return value->get_date(ltime, fuzzydate);
+  }
+  else
+  {
+    reset();
+    return 0;
+  }
+}
+
+
 Item_exists_subselect::Item_exists_subselect(st_select_lex *select_lex):
   Item_subselect()
 {

sql/item_subselect.h

@@ -275,6 +275,7 @@ class Item_singlerow_subselect :public Item_subselect
   String *val_str (String *);
   my_decimal *val_decimal(my_decimal *);
   bool val_bool();
+  bool get_date(MYSQL_TIME *ltime,uint fuzzydate);
   enum Item_result result_type() const;
   enum_field_types field_type() const;
   void fix_length_and_dec();