1 files changed, 19 insertions, 11 deletions

diff --git a/sql/item_timefunc.cc b/sql/item_timefunc.cc
index 0d652a431cb..80563b9cc83 100644
--- a/sql/item_timefunc.cc
+++ b/sql/item_timefunc.cc
@@ -1656,6 +1656,7 @@ void Item_func_convert_tz::fix_length_and_dec()
   collation.set(&my_charset_bin);
   decimals= 0;
   max_length= MAX_DATETIME_WIDTH*MY_CHARSET_BIN_MB_MAXLEN;
+  maybe_null= 1;
 }
 
 
@@ -1668,12 +1669,6 @@ Item_func_convert_tz::fix_fields(THD *thd_arg, TABLE_LIST *tables_arg, Item **re
 
   tz_tables= thd_arg->lex->time_zone_tables_used;
 
-  if (args[1]->const_item())
-    from_tz= my_tz_find(args[1]->val_str(&str), tz_tables);
-
-  if (args[2]->const_item())
-    to_tz= my_tz_find(args[2]->val_str(&str), tz_tables);
-
   return 0;
 }
 
@@ -1713,13 +1708,19 @@ bool Item_func_convert_tz::get_date(TIME *ltime,
   my_time_t my_time_tmp;
   bool not_used;
   String str;
-  
-  if (!args[1]->const_item())
+
+  if (!from_tz_cached)
+  {
     from_tz= my_tz_find(args[1]->val_str(&str), tz_tables);
-  
-  if (!args[2]->const_item())
+    from_tz_cached= args[1]->const_item();
+  }
+
+  if (!to_tz_cached)
+  {
     to_tz= my_tz_find(args[2]->val_str(&str), tz_tables);
-  
+    to_tz_cached= args[2]->const_item();
+  }
+
   if (from_tz==0 || to_tz==0 || get_arg0_date(ltime, 0))
   {
     null_value= 1;
@@ -1741,6 +1742,13 @@ bool Item_func_convert_tz::get_date(TIME *ltime,
 }
 
 
+void Item_func_convert_tz::cleanup()
+{
+  from_tz_cached= to_tz_cached= 0;
+  Item_date_func::cleanup();
+}
+
+
 void Item_date_add_interval::fix_length_and_dec()
 {
   enum_field_types arg0_field_type;