mysql 比较两个日期的时间差

1 DATEDIFF 函数

 这个默认以天为时间差，不能更改时间格式，不是很灵活。

SELECT TIMESTAMPDIFF (HOUR,"2021-04-21 23:23:12","2021-04-25 23:23:12") as d

2 TIMESTAMPDIFF 函数

这就可以区分时间级别

天（DAY）、小时（HOUR），分钟（MINUTE）和秒（SECOND）

SELECT TIMESTAMPDIFF (DAY,"2021-04-21 23:23:12","2021-04-25 23:23:12") as "天"
SELECT TIMESTAMPDIFF (HOUR,"2021-04-21 23:23:12","2021-04-25 23:23:12") as "时"
SELECT TIMESTAMPDIFF (MINUTE,"2021-04-21 23:23:12","2021-04-25 23:23:12") as "分"
SELECT TIMESTAMPDIFF (SECOND,"2021-04-21 23:23:12","2021-04-25 23:23:12") as "秒"