We don't need tmp_value member in the Item_func_left.

sql/item_strfunc.cc

@@ -952,8 +952,8 @@ String *Item_func_left::val_str(String *str)
     return &my_empty_string;
   if (res->length() <= (uint) length)
     return res;
-  tmp_value.set(*res, 0, res->charpos(length));
-  return &tmp_value;
+  str_value.set(*res, 0, res->charpos(length));
+  return &str_value;
 }
 
 

sql/item_strfunc.h

@@ -180,7 +180,6 @@ public:
 
 class Item_func_left :public Item_str_func
 {
-  String tmp_value;
 public:
   Item_func_left(Item *a,Item *b) :Item_str_func(a,b) {}
   String *val_str(String *);