SQLServer自訂函數——fnSumOfTwoTime

/*************************************************************
** File: fnSumOfTwoTime.sql
** Name: fnSumOfTwoTime
** Description: 把兩個以“小時:分鐘:秒鐘”的時間相加求和
  輸入參數必須以24小時格式來表示且不能為“24:00:00”
** Return values: varchar(20) 
** Parameters: @dtmStart,@dtmEnd
** Author: 何毅翔(MyGodness)
** Date: 2005-4-6
** Use method: select dbo.fnSumOfTwoTime('9:00:00','13:15:22')
*************************************************************/
Create function fnSumOfTwoTime(@a varchar(8),@b varchar(8))
returns varchar(20)
As
Begin
 declare @sum datetime
 select @sum=convert(datetime,@a)+convert(datetime,@b)
 return cast(cast(day(@sum)-1 as int)*24+DATEPART(hh,@sum) as varchar)+':'+cast(DATEPART(n,@sum) as varchar)+':'+cast(DATEPART(s,@sum) as varchar)
End