datediff用法

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