返回在指定日期内有几个指定的星期数

GO

if exists (select null from sysobjects where [name] = 'fn_get_weekday_num')

     drop function fn_get_weekday_num

GO

/*===================================================================================================

功能: 返回在指定日期内有几个指定的星期数  

       ( 如: 计算出在 2006-07-01 --> 2006-07-31 之间有几个 星期日 )

参数说明:

         @strat_date   日期范围的开始日期 

         @end_date     日期范围的结束日期

         @weekday      星期数 (范围:1-7 )

                            1   =    星期一  

                            2   =    星期二  

                            3   =    星期三  

                            4   =    星期四  

                            5   =    星期五  

                            6   =    星期六  

                            7   =    星期日

例: 

     select dbo.fn_get_weekday_num ('2006-07-01','2006-07-31',7) 

===================================================================================================*/

create function dbo.fn_get_weekday_num(@strat_date datetime   ,@end_date datetime   , @weekday int)

returns int

as 

begin

     ------------------------------------------------------------------------------------------------

     /*定义变量*/

     declare @return_value   int 

     declare @start_weekday int ,@end_weekday int

     ------------------------------------------------------------------------------------------------

     /*根据系统 DATEFIRST 计算出星期*/

     set @weekday =   case when @weekday >= @@datefirst   then @weekday- @@datefirst+1

                       else @weekday + 8 - @@datefirst end

     /*计算出开始日期与结束日期分别为星期几*/

     set @start_weekday = datepart(weekday,@strat_date)

     set @end_weekday    = datepart(weekday,@end_date)

     ------------------------------------------------------------------------------------------------

     /*计算时间范围内有几个指定的星期数*/    

     select   @return_value=   datediff(day , @strat_date,@end_date)/7

             +case when @start_weekday > @end_weekday 

                   then case when (@weekday <= 7   and   @weekday >= @start_weekday)

                                   or ( @weekday >= 1 and   @weekday <= @end_weekday)

                             then 1 else 0 end

              else case when      ( @weekday >= @start_weekday  

                                  and   @weekday <= @end_weekday)            

                  then 1 else 0 end

             end

     ------------------------------------------------------------------------------------------------

     /*返回值*/

     return @return_value

end

GO