MYSQL自定义函数之返回两个时间的指定类型时差

DELIMITER $$

CREATE FUNCTION DateBetween
 (AType INT, ADateStart DATETIME, ADateEnd DATETIME)
RETURNS BIGINT
BEGIN
DECLARE AResult BIGINT DEFAULT -1;
/*入参AType INT类型，结果类型 1:年 2:月 3:日 4:小时 5:分钟 6:秒钟 (必须在1-6内，否则结果返回-1)
*入参ADateStart DATETIME类型，起始时间 (必须是一个正确的日期参数)
*入参ADateEnd DATETIME类型，结束时间 (必须是一个正确的日期参数)
*返回值 BIGINT类型，返回起始之间与结束时间的指定时差 (成功返回计算出的时差，失败返回-1)
*/
IF ADateStart != '' AND ADateEnd != '' AND AType >=1 AND AType <= 6 THEN
 CASE AType
 WHEN 1 THEN
 SELECT TIMESTAMPDIFF(YEAR, ADateStart, ADateEnd) INTO AResult; 
 WHEN 2 THEN 
 SELECT TIMESTAMPDIFF(MONTH, ADateStart, ADateEnd) INTO AResult; 
 WHEN 3 THEN
 SELECT TIMESTAMPDIFF(DAY, ADateStart, ADateEnd) INTO AResult; 
 WHEN 4 THEN
 SELECT TIMESTAMPDIFF(HOUR, ADateStart, ADateEnd) INTO AResult; 
 WHEN 5 THEN
 SELECT TIMESTAMPDIFF(MINUTE, ADateStart, ADateEnd) INTO AResult; 
 WHEN 6 THEN
 SELECT TIMESTAMPDIFF(SECOND, ADateStart, ADateEnd) INTO AResult; 
 END CASE;
END IF;
RETURN(AResult); 
END$$

SELECT DateBetween(0, '2010-01-01 00:00:00', '2010-01-01 10:00:00');
SELECT DateBetween(1, '2001-01-01', '2010-01-01');
SELECT DateBetween(2, '2010-01-01', '2010-12-01');
SELECT DateBetween(3, '2010-01-01', '2010-01-31');
SELECT DateBetween(4, '2010-01-01 00:00:00', '2010-01-01 10:00:00');
SELECT DateBetween(5, '2010-01-01 00:00:00', '2010-01-01 10:00:00');
SELECT DateBetween(6, '2010-01-01 00:00:00', '2010-01-01 10:00:00');
SELECT DateBetween(7, '2010-01-01 00:00:00', '2010-01-01 10:00:00');