1.loop
语法：

[begin_label:] LOOP
    statement_list
END LOOP [end_label]

例子：
CREATE PROCEDURE doiterate(p1 INT)
BEGIN
  label1: LOOP
    SET p1 = p1 + 1;
    IF p1 < 10 THEN
      ITERATE label1;// ITERATE can appear only within LOOP, REPEAT, and WHILE statements. ITERATE means “start the loop again.”
    END IF;
    LEAVE label1;// LEAVE can be used within BEGIN ... END or loop constructs (LOOP, REPEAT, WHILE).
  END LOOP label1;
  SET @x = p1;
END;
2.repeat 
语法

[begin_label:] REPEAT
    statement_list
UNTIL search_condition
END REPEAT [end_label]

例子：

mysql> delimiter //

mysql> CREATE PROCEDURE dorepeat(p1 INT)
    -> BEGIN
    ->   SET @x = 0;
    ->   REPEAT
    ->     SET @x = @x + 1;
    ->   UNTIL @x > p1 END REPEAT;
    -> END
    -> //
Query OK, 0 rows affected (0.00 sec)

mysql> CALL dorepeat(1000)//
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @x//
+------+
| @x   |
+------+
| 1001 |
+------+
1 row in set (0.00 sec)

3.while
语法

[begin_label:] WHILE search_condition DO
    statement_list
END WHILE [end_label]

例子：

CREATE PROCEDURE dowhile()
BEGIN
  DECLARE v1 INT DEFAULT 5;

  WHILE v1 > 0 DO
    ...
    SET v1 = v1 - 1;
  END WHILE;
END;

4.label标记语法

[begin_label:] BEGIN
    [statement_list]
END [end_label]

[begin_label:] LOOP
    statement_list
END LOOP [end_label]

[begin_label:] REPEAT
    statement_list
UNTIL search_condition
END REPEAT [end_label]

[begin_label:] WHILE search_condition DO
    statement_list
END WHILE [end_label]