Loop in MySQL stored procedure

There are three standard loops in the MySQL stored procedure statement: WHILE loop, LOOP loop and REPEAT loop. There is also a non-standard looping method: GOTO, but this looping method is best not to use, it is easy to cause confusion in the program, here is a good introduction.

The format of these loop statements is as follows:
WHILE ... DO ... END WHILE
REPEAT ... UNTIL END REPEAT
LOOP ... END LOOP
GOTO.

Let's first write an example using the first loop.

DROP PROCEDURE IF EXISTS `pro10`;
DELIMITER $$
CREATE PROCEDURE `pro10`()
BEGIN
    -Define variables
    DECLARE v_i int unsigned DEFAULT 0;
    WHILE v_i < 5 DO
        SELECT v_i;
        SET v_i = v_i+1;
    END WHILE;
END $$
DELIMITER ;

CALL pro10();

Let's take a look at the second loop control instruction REPEAT ... END REPEAT. Use the REPEAT loop control statement to write the following stored procedure:

DROP PROCEDURE IF EXISTS `pro11`;
DELIMITER $$
CREATE PROCEDURE `pro11`()
BEGIN
    -Define variables
    DECLARE v_i int unsigned DEFAULT 0;
    REPEAT
        SELECT v_i;
        SET v_i = v_i+1;
    UNTIL v_i >= 5 END REPEAT;
END $$
DELIMITER ;

CALL pro11();

Let's take a look at the third loop control statement LOOP ...... END LOOP. Write a stored procedure program as follows:

DROP PROCEDURE IF EXISTS `pro12`;
DELIMITER $$
CREATE PROCEDURE `pro12`()
BEGIN
    -Define variables
    DECLARE v_i int unsigned DEFAULT 0;
    LOOP_LABEL:LOOP
        SELECT v_i;
        SET v_i = v_i+1;
        IF v_i >= 5 THEN
            LEAVE LOOP_LABEL;
        END IF;
    END LOOP;
END $$
DELIMITER ;

CALL pro12();

DROP PROCEDURE IF EXISTS `pro13`;
DELIMITER $$
CREATE PROCEDURE `pro13`()
BEGIN
    -Define variables
    DECLARE v_i int unsigned DEFAULT 0;
    LOOP_LABEL:LOOP
        IF v_i = 3 THEN
            SET v_i = v_i+1;
            ITERATE LOOP_LABEL; # => continue
        END IF;
        SELECT v_i;
        SET v_i = v_i+1;
        IF v_i >= 5 THEN
            LEAVE LOOP_LABEL; # => break;
        END IF;
    END LOOP;
END $$
DELIMITER ;

CALL pro13();