fixed bug in subselect value storing

mysql-test/r/subselect.result:
  test for bug in subselect value storing
mysql-test/t/subselect.test:
  test for bug in subselect value storing

mysql-test/r/subselect.result

@@ -159,6 +159,9 @@ UNIQUE KEY `email` (`email`)
 INSERT INTO inscrit (pseudo,email) VALUES ('joce','test');
 INSERT INTO inscrit (pseudo,email) VALUES ('joce1','test1');
 INSERT INTO inscrit (pseudo,email) VALUES ('2joce1','2test1');
+SELECT pseudo FROM inscrit WHERE pseudo=(SELECT pseudo FROM inscrit WHERE pseudo='joce');
+pseudo
+joce
 SELECT pseudo FROM inscrit WHERE pseudo=(SELECT pseudo FROM inscrit WHERE pseudo LIKE '%joce%');
 Subselect returns more than 1 record
 drop table if exists t1,t2,t3,t4,t5,attend,clinic,inscrit;

mysql-test/t/subselect.test

@@ -82,6 +82,7 @@ CREATE TABLE `inscrit` (
 INSERT INTO inscrit (pseudo,email) VALUES ('joce','test');
 INSERT INTO inscrit (pseudo,email) VALUES ('joce1','test1');
 INSERT INTO inscrit (pseudo,email) VALUES ('2joce1','2test1');
+SELECT pseudo FROM inscrit WHERE pseudo=(SELECT pseudo FROM inscrit WHERE pseudo='joce');
 -- error 1240
 SELECT pseudo FROM inscrit WHERE pseudo=(SELECT pseudo FROM inscrit WHERE pseudo LIKE '%joce%');
 

sql/item_subselect.cc

@@ -150,6 +150,8 @@ String *Item_singleval_subselect::val_str (String *str)
     assign_null();
     return 0;
   }
+  // Assign temporary buffer with stored value
+  str_value.set(string_value, 0, string_value.length());
   return &str_value;
 }
 

sql/item_subselect.h

@@ -80,10 +80,16 @@ class Item_subselect :public Item
 class Item_singleval_subselect :public Item_subselect
 {
 protected:
-  longlong int_value; /* here stored integer value of this item */
-  double real_value; /* here stored real value of this item */
+  longlong int_value; /* Here stored integer value of this item */
+  double real_value; /* Here stored real value of this item */
+  /* 
+     Here stored string value of this item.
+     (str_value used only as temporary buffer, because it can be changed 
+     by Item::save_field)
+  */
+  String string_value; 
   enum Item_result res_type; /* type of results */
-
+  
 public:
   Item_singleval_subselect(THD *thd, st_select_lex *select_lex);
   Item_singleval_subselect(Item_singleval_subselect *item):
@@ -91,6 +97,7 @@ class Item_singleval_subselect :public Item_subselect
   {
     int_value= item->int_value;
     real_value= item->real_value;
+    string_value.set(item->string_value, 0, item->string_value.length());
     max_length= item->max_length;
     decimals= item->decimals;
     res_type= item->res_type;

sql/sql_class.cc

@@ -884,9 +884,14 @@ bool select_singleval_subselect::send_data(List<Item> &items)
     it->decimals= val_item->decimals;
     it->binary= val_item->binary;
     it->int_value= val_item->val_int();
-    String *s= val_item->val_str(&it->str_value);
-    if (s != &it->str_value)
-      it->str_value.set(*s, 0, s->length());
+    String *s= val_item->val_str(&it->string_value);
+    if (s != &it->string_value)
+    {
+      it->string_value.set(*s, 0, s->length());
+    }
+    // TODO: remove when correct charset handling appeared for Item
+    it->str_value.set(*s, 0, s->length()); // store charset
+
     it->res_type= val_item->result_type();
   }
   it->assigned(1);