A fix (bug #5540: CONCAT function and 'double' type).

mysql-test/r/func_concat.result

@@ -26,3 +26,9 @@ FROM t1 GROUP BY new LIMIT 1;
 number	alpha	new
 1413006	idlfmv	1413006<------------------>idlfmv
 drop table t1;
+create table t1 (a char(4), b double, c date, d tinyint(4));
+insert into t1 values ('AAAA', 105, '2003-03-01', 1);
+select * from t1 where concat(A,C,B,D) = 'AAAA2003-03-011051';
+a	b	c	d
+AAAA	105	2003-03-01	1
+drop table t1;

mysql-test/t/func_concat.test

@@ -25,3 +25,12 @@ FROM t1 GROUP BY new LIMIT 1;
 SELECT number, alpha, CONCAT_WS('<------------------>',number,alpha) AS new
 FROM t1 GROUP BY new LIMIT 1;
 drop table t1;
+
+#
+# Bug #5540: a problem with double type
+#
+
+create table t1 (a char(4), b double, c date, d tinyint(4));
+insert into t1 values ('AAAA', 105, '2003-03-01', 1);
+select * from t1 where concat(A,C,B,D) = 'AAAA2003-03-011051';
+drop table t1;

sql/item_strfunc.cc

@@ -289,7 +289,8 @@ String *Item_func_concat::val_str(String *str)
 	  str->copy(*res);
 	  str->append(*res2);
 	}
-	res=str;
+        res= str;
+        use_as_buff= &tmp_value;
       }
       else if (res == &tmp_value)
       {