A fix for a crashing bug #7101, which occures when the

expression involving LEFT() function is used in GROUP BY
field.

mysql-test/r/func_str.result

@@ -685,3 +685,9 @@ drop table t1;
 select left(1234, 3) + 0;
 left(1234, 3) + 0
 123
+create table t1 (a int not null primary key, b varchar(40), c datetime);
+insert into t1 (a,b,c) values (1,'Tom',now()),(2,'ball games',now()), (3,'Basil',now()), (4,'Dean',now()),(5,'Ellis',now()), (6,'Serg',now()), (7,'Sergei',now()),(8,'Georg',now()),(9,'Salle',now()),(10,'Sinisa',now());
+select count(*) as total, left(c,10) as reg from t1 group by reg order by reg desc limit 0,12;
+total	reg
+10	2004-12-10
+drop table t1;

mysql-test/t/func_str.test

@@ -421,3 +421,11 @@ drop table t1;
 #
 
 select left(1234, 3) + 0;
+
+#
+# Bug #7101: bug with LEFT() when used as a field in GROUP BY aggregation
+#
+create table t1 (a int not null primary key, b varchar(40), c datetime);
+insert into t1 (a,b,c) values (1,'Tom',now()),(2,'ball games',now()), (3,'Basil',now()), (4,'Dean',now()),(5,'Ellis',now()), (6,'Serg',now()), (7,'Sergei',now()),(8,'Georg',now()),(9,'Salle',now()),(10,'Sinisa',now()); 
+select count(*) as total, left(c,10) as reg from t1 group by reg order by reg desc limit 0,12;
+drop table t1;

sql/item_strfunc.cc

@@ -955,8 +955,9 @@ String *Item_func_left::val_str(String *str)
   if (res->length() <= (uint) length ||
       res->length() <= (char_pos= res->charpos(length)))
     return res;
-  str_value.set(*res, 0, char_pos);
-  return &str_value;
+
+  tmp_value.set(*res, 0, char_pos);
+  return &tmp_value;
 }
 
 

sql/item_strfunc.h

@@ -162,6 +162,7 @@ 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 *);