mysql存储过程之循环语句（WHILE，REPEAT和LOOP）用法分析

WHILE expression DO
  statements
END WHILE

DELIMITER $$
 DROP PROCEDURE IF EXISTS test_mysql_while_loop$$
 CREATE PROCEDURE test_mysql_while_loop()
 BEGIN
 DECLARE x INT;
 DECLARE str VARCHAR(255);
 SET x = 1;
 SET str = '';
 WHILE x <= 5 DO
 SET str = CONCAT(str,x,',');
 SET x = x + 1; 
 END WHILE;
 SELECT str;
 END$$
DELIMITER ;

CALL test_mysql_while_loop();

mysql> CALL test_mysql_while_loop();
+------------+
| str    |
+------------+
| 1,2,3,4,5, |
+------------+
1 row in set
Query OK, 0 rows affected

REPEAT
 statements;
UNTIL expression
END REPEAT

DELIMITER $$
 DROP PROCEDURE IF EXISTS mysql_test_repeat_loop$$
 CREATE PROCEDURE mysql_test_repeat_loop()
 BEGIN
 DECLARE x INT;
 DECLARE str VARCHAR(255);
 SET x = 1;
    SET str = '';
 REPEAT
 SET str = CONCAT(str,x,',');
 SET x = x + 1;
    UNTIL x > 5
    END REPEAT;
    SELECT str;
 END$$
DELIMITER ;

mysql> CALL mysql_test_repeat_loop();
+------------+
| str    |
+------------+
| 1,2,3,4,5, |
+------------+
1 row in set
Query OK, 0 rows affected

CREATE PROCEDURE test_mysql_loop()
 BEGIN
 DECLARE x INT;
    DECLARE str VARCHAR(255);
 SET x = 1;
    SET str = '';
 loop_label: LOOP
 IF x > 10 THEN 
 LEAVE loop_label;
 END IF;
 SET x = x + 1;
 IF (x mod 2) THEN
   ITERATE loop_label;
 ELSE
  SET str = CONCAT(str,x,',');
 END IF;
  END LOOP;
  SELECT str;
END;

mysql> CALL test_mysql_loop();
+-------------+
| str     |
+-------------+
| 2,4,6,8,10, |
+-------------+
1 row in set
Query OK, 0 rows affected