--1、相差天数 
select trunc(sysdate,'yyyy')-to_date('2009-01-04','yyyy-mm-dd') from dual;

--2、相差月数 
select  months_between(trunc(sysdate,'mm'),to_date('2009-01','yyyy-mm')) from dual;

--3、相差年数 
select trunc((months_between(trunc(sysdate,'dd'),to_date('2009-01-01','yyyy-mm-dd')))/12) from dual;

--4、
select datediff( day, '2008.08.25', '2008.09.01' )

--5、
select datediff( second, '2009-8-25 12:15:12', '2009-9-1 7:18:20') --返回相差秒数

--6、
select datediff( minute, '2009-8-25 12:15:12', '2009-9-1 7:18:20') --返回相差分钟数

--7、
select datediff( hour, '2009-8-25 12:15:12', 2009-9-1 7:18:20') --返回相差小时数

--问题三：select datediff( day, 2009-8-25 12:15:12', 2009-9-1 7:18:20')

--8、
SELECT  (CAST(datediff(second,StartDate,EndDate) AS FLOAT)/60)AS D 
FROM Inventory WHERE RecordId = 2292549  --获取两个日期之差（单位 M）

use pubs 
select distinct datediff(day, '2009-3-12', '2009-3-15') as difday 
from titles

select t1.*,t2.RESPONSE_TIME from dbo.CO_ALARM_RECORD t1,dbo.CO_WORK_THRESHOLD t2 where t2.alarm_type_id=t1.alarm_type and datediff( minute, alarm_time, complete_time)>5 
declare @dt1 as datetime, @dt2 as datetime; 
select @dt1 = '2008-8-4 9:36:41', @dt2 = '2008-8-2 9:33:39'; 
declare @days as int, @hours as int, @minutes as int, @seconds as int; 
set @seconds = datediff( second, @dt2, @dt1); 
set @days = @seconds / (24 * 60 * 60) 
set @seconds = @seconds - @days * 24 * 60 * 60 
set @hours = @seconds / (60 * 60); 
set @seconds = @seconds - @hours * 60 * 60 
set @minutes = @seconds / 60; 
set @seconds = @seconds - @minutes * 60; 
select convert(varchar(10), @days ) + '天' + convert(varchar(10), @hours ) + '小时' + convert(varchar(10), @minutes ) + '分' + convert(varchar(10), @seconds ) + '秒';

declare @t table 
( 
beginday int, 
begintime varchar(20), 
endday int, 
endtime varchar(20) 
) 
insert @t select 1,'16:00',2,'12:20' 
union all select 1,'3:00',3,'19:10' 
select 
    date=rtrim(date/60)+':'+rtrim(date`) 
from 
(select     date=datediff(mi,1,dateadd(d,endday-beginday,beginday)-begintime+endtime)from    @t )t 
date 
------------------------- 
20:20 
64:10

declare @t table(开始天数 varchar(10),开始时间 varchar(10),到达天数 varchar(10),到达时间 varchar(10)) 
insert @t select '1',  '16:00','2','12:20' 
--如果开始天数，到达天数大于31 
select 到达天数 * 24 + datepart(hh,到达时间) - 开始天数 * 24 - datepart(hh,开始时间) 
from @t