select NOW(),CURRENT_TIMESTAMP(),SYSDATE()
2021-08-06 18:27:31.0 2021-08-06 18:27:31.0 2021-08-06 18:27:31.0

select NOW(3),CURRENT_TIMESTAMP(3),SYSDATE(3);
2021-08-06 18:28:42.543 2021-08-06 18:28:42.543 2021-08-06 18:28:42.543

秒后边的小数位数，最大为6，表示精确到微秒级别，默认为0，表示精确到秒

select NOW(),CURRENT_TIMESTAMP(),SYSDATE(),CURRENT_DATE() ,UNIX_TIMESTAMP() 

2021-08-11 08:47:33.0
2021-08-11 08:47:33.0
2021-08-11 08:47:33.0
2021-08-11
1628642853





SELECT CURRENT_DATE() 
2021-08-06

SELECT UNIX_TIMESTAMP() 
自'1970-01-01 00:00:00' 到当前时间的秒数差

SELECT UNIX_TIMESTAMP('2021-08-06') 
1628179200

SELECT UNIX_TIMESTAMP('2021-08-06 08:08:08')
1628208488


SELECT UNIX_TIMESTAMP(NOW()) 
1628238758

SELECT UNIX_TIMESTAMP(NOW(3)) 
1628238774.082

SELECT UNIX_TIMESTAMP(NOW(6)) 
1628238799.139291