该函数在MYSQL下编写，5.1版本测试通过。

函数需要传入三个参数，类型(用于区别应返回时差年、时差月...时差秒)，起始时间(用于计算)，结束时间(用于计算)

1.[代码]DateBetween函数

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$$

2.[代码]测试用例

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');