本文供应了SQL Server中的DATEDIFF()函数的运用示例。
DATEDIFF()函数语法以下:
DATEDIFF ( datepart , startdate , enddate )
个中datepart是你想要比较的日期的一部份。startdate是第一个日期,enddate是完毕日期。
它的工作方式是从enddate中减去startdate。
示例1
下面是一个基础的例子,我们可以算出两个日期之间的天数:
SELECT DATEDIFF(day, '2001-01-01', '2002-01-01') AS Result;
效果:
+----------+ | Result | |----------| | 365 | +----------+
示例2
下面是另一个例子,我声清楚明了两个变量并为它们分配了两个差别的日期(我运用DATEADD()将第一个日期增加1年)。然后运用DATEDIFF()返回该日期的各个dateparts:
DECLARE @date1 datetime2 = '2000-01-01 00:00:00.0000000'; DECLARE @date2 datetime2 = DATEADD(year, 1, @date1); SELECT DATEDIFF( year, @date1, @date2 ) AS Years, DATEDIFF( quarter, @date1, @date2 ) AS Quarters, DATEDIFF( month, @date1, @date2 ) AS Months, DATEDIFF( week, @date1, @date2 ) AS Weeks, DATEDIFF( dayofyear, @date1, @date2 ) AS DayOfYear, DATEDIFF( day, @date1, @date2 ) AS Days;
效果:
+---------+------------+----------+---------+-------------+--------+ | Years | Quarters | Months | Weeks | DayOfYear | Days | |---------+------------+----------+---------+-------------+--------| | 1 | 4 | 12 | 53 | 366 | 366 | +---------+------------+----------+---------+-------------+--------+
示例3
如前所述,你还可以返回日期之间的时候部份。下面是返回日期/时候值之间的小时、分钟和秒数的例子:
DECLARE @date1 datetime2 = '2000-01-01 00:00:00.0000000'; DECLARE @date2 datetime2 = DATEADD(hour, 1, @date1); SELECT DATEDIFF( hour, @date1, @date2 ) AS Hours, DATEDIFF( minute, @date1, @date2 ) AS Minutes, DATEDIFF( second, @date1, @date2 ) AS Seconds;
效果:
+---------+-----------+-----------+ | Hours | Minutes | Seconds | |---------+-----------+-----------| | 1 | 60 | 3600 | +---------+-----------+-----------+
示例4
下面是一个猎取两个日期/时候值之间的毫秒、微秒和纳秒数的例子:
DECLARE @date1 datetime2 = '2000-01-01 00:00:00.0000000'; DECLARE @date2 datetime2 = DATEADD(millisecond, 1, @date1); SELECT DATEDIFF( millisecond, @date1, @date2 ) AS Milliseconds, DATEDIFF( microsecond, @date1, @date2 ) AS Microseconds, DATEDIFF( nanosecond, @date1, @date2 ) AS Nanoseconds;
效果:
+----------------+----------------+---------------+ | Milliseconds | Microseconds | Nanoseconds | |----------------+----------------+---------------| | 1 | 1000 | 1000000 | +----------------+----------------+---------------+
示例5 - Error毛病!
假如你尝试做一些极度的事变,比方,返回100年后的纳秒数,你会获得一个毛病。这是由于DATEDIFF()返回一个int值,100年内的纳秒数比int数据类型可以处置惩罚的纳秒数还要多。
假如你试着这么做会发作什么呢?
DECLARE @date1 datetime2 = '2000-01-01 00:00:00.0000000'; DECLARE @date2 datetime2 = DATEADD(year, 100, @date1); SELECT DATEDIFF( millisecond, @date1, @date2 ) AS Milliseconds, DATEDIFF( microsecond, @date1, @date2 ) AS Microseconds, DATEDIFF( nanosecond, @date1, @date2 ) AS Nanoseconds;
效果:
The datediff function resulted in an overflow. The number of dateparts separating two date/time instances is too large. Try to use datediff with a less precise datepart.
固然假如你真的必需找出100年内有多少纳秒,那末可以运用DATEDIFF_BIG()函数。这个函数返回一个带符号的bigint数据类型,它许可你返回比DATEDIFF()更大的值。
相干引荐:《MySQL教程》
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