涉及的函式
date_format(date, format) 函式
unix_timestamp() 函式
str_to_date(str, format) 函式
from_unixtime(unix_timestamp, format) 函式

1.字串轉化成時間
select
str_to_date('2019-09-12 00:16:50','%Y-%m-%d %H:%i:%s'),
str_to_date('2019-09-12 00:16:50','%Y-%m-%d %H')

2019-09-12 00:16:50    2019-09-12 00:00:00

2.字串轉化成時間戳
select
unix_timestamp('2019-09-12 00:00:50'),

1568217650    1568217660

3.時間轉換成字串
select
date_format(now(), '%Y-%m-%d'),
date_format(now(), '%Y-%m-%d %H:%i:%s')

2020-08-24    2020-08-24 14:51:26

4.時間轉換成時間戳
select
unix_timestamp(now());

1598251906

5.時間戳轉換成時間
select from_unixtime(1598250986);

2020-08-24 14:36:26

6.時間戳轉成成字串

2020-08-24

要想獲得正確的時間相減秒數，有以下三張方式：
1、time_to_sec(timediff(t2, t1))
2、timestampdiff(second, t1, t2)
3、unix_timestamp(t2) -unix_timestamp(t1)


列子：
select time_to_sec(timediff(str_to_date('2019-09-12 00:17:50','%Y-%m-%d %H:%i:%s'), str_to_date('2019-09-12 00:16:50','%Y-%m-%d %H:%i:%s')))

60

select timestampdiff(second, str_to_date('2019-09-12 00:17:50','%Y-%m-%d %H:%i:%s'), str_to_date('2019-09-12 00:16:50','%Y-%m-%d %H:%i:%s'))

-60

select unix_timestamp(str_to_date('2019-09-12 00:17:50','%Y-%m-%d %H:%i:%s')) -unix_timestamp(str_to_date('2019-09-12 00:16:50','%Y-%m-%d %H:%i:%s'))

60