目录
datediff是SQL SERVER里面的用法，ORACLE没有
一、作用：返回两个日期之间的时间间隔
二、语法：datediff(datepart,startdate,enddate)
是后面日期减去前面的日期(enddate-startdate)
1、datepart，规定应在日期的哪一部分计算差额
日期 缩写
year yy/yyyy
quarter qq/q
Month mm/m
day dd/d
Hour hh/h
minute mi,n
second ss,s
三、测试
SQL SERVER不用像ORACLE一样写 select ... from dual，只需要写select ....就可以了
1、参数是 yyyy的话，统计相差的年份，截取前4位进行统计
select datediff(yyyy,'20210928','20200121')test --select datediff(year,'20210928','20200121')test --select datediff(yy,'20210928','20200121')test
2、参数是 qq时，统计相差的季度
select datediff(qq,'20210928','20200121')test --select datediff(q,'20210928','20200121')test --select datediff(quarter,'20210928','20200121')test
3、参数是 mm的时候，统计相差的月份，截取前6位进行统计
select datediff(mm,'20210928','20200121')test --select datediff(m,'20210928','20200121')test --select datediff(month,'20210928','20200121')test
4、参数是 dd的时候，统计相差的天数
select datediff(dd,'20210928','20200121')test --select datediff(day,'20210928','20200121')test --select datediff(d,'20210928','20200121')test
5、参数是 hh的时候，统计相差的小时
select datediff(hour,'20211112 10:00:00','20211112 00:00:00')test_hour
,datediff(hh,'20211112 10:00:00','20211112 00:00:00')test_hh
6、参数是 mi的时候，统计相差的分钟数
select datediff(minute,'20211112 10:00:00','20211112 00:00:00')test_minute
,datediff(mi,'20211112 10:00:00','20211112 00:00:00')test_mi
,datediff(n,'20211112 10:00:00','20211112 00:00:00')test_n
7、参数是 ss的时候，统计相差的秒数
select datediff(second,'20211112 10:00:00','20211112 00:00:00')test_second
,datediff(ss,'20211112 10:00:00','20211112 00:00:00')test_ss
,datediff(s,'20211112 10:00:00','20211112 00:00:00')test_s
