T-SQL:三个通用的与日期相关的,辅助按周(星期日是周的最后一天)汇总的自定义函数

/*
每个函数都只有一句话!
其实都是从我的另一篇 blog 里抠出来的:

T-SQL 生成 两个新的真正的公历年历
http://blog.csdn.net/playyuer/archive/2004/04/07/2860.aspx

T-SQL 生成一个简易的 公历年历 T-SQL 含日期所在月及年的周次
http://blog.csdn.net/playyuer/archive/2004/04/05/2859.aspx

由于使用了 (@@datefirst + datepart(weekday,@date)) % 7  判断周几
因此与 datefirst 无关,且可适应各种语言版本的 SQL Server

*/

--周日算作(上一)周的最后一天

create function udf_WeekOfYear(@date datetime)
--求 @date 所在周是当年的第几周
--周日算作(上一)周的最后一天
--用于按周汇总 Group by 时,不要有跨年数据,或者同时 Group by year
--group by year(date),month(date), dbo.udf_WeekOfYear(date),dbo.udf_WeekOfMonth(date)
returns int
as
begin
return
(select datediff(week
                 ,case when (@@datefirst + datepart(weekday,dateadd(day,0,datediff(day,0,dateadd(year,datediff(year,0,@date),0))))) % 7 = 1
                            then dateadd(day,-1,dateadd(day,0,datediff(day,0,dateadd(year,datediff(year,0,@date),0))))
                       else dateadd(day,0,datediff(day,0,dateadd(year,datediff(year,0,@date),0))) --date 所在年的第一天 即: 一月一号
                  end
                 ,case when (@@datefirst + datepart(weekday,@date)) % 7 = 1
                            then dateadd(day,-1,@date)
                       else @date
                  end
                ) + 1)
end

go

create function udf_WeekOfMonth(@date datetime)
--求 @date 所在周是当月的第几周
--周日算作(上一)周的最后一天
--用于按周汇总 Group by 时,不要有跨月跨年数据,或者同时 Group by year,month
--group by year(date),month(date), dbo.udf_WeekOfYear(date),dbo.udf_WeekOfMonth(date)
returns int
as
begin
return
      ( select datediff(week
                 ,case when (@@datefirst + datepart(weekday,dateadd(month,datediff(month,0,@date),0))) % 7 = 1
                            then dateadd(month,datediff(month,0,@date),0) - 1
                       else dateadd(month,datediff(month,0,@date),0)
                  end
                 ,case when (@@datefirst + datepart(weekday,@date)) % 7 = 1
                            then @date-1
                       else @date
                  end
                ) + 1 )
end

go

create function udf_weekday(@ int,@date datetime)
returns datetime
as
begin
/*
--周日算作(上一)周的最后一天
  当 @ <= 1 代表将 @date 映射到 所在周的星期一
  当 @ = 2  代表将 @date 映射到 所在周的星期二
  当 @ = 3  代表将 @date 映射到 所在周的星期三
  当 @ = 4  代表将 @date 映射到 所在周的星期四
  当 @ = 5  代表将 @date 映射到 所在周的星期五
  当 @ = 6  代表将 @date 映射到 所在周的星期六
  当 @ >= 7 代表将 @date 映射到 所在周的星期日
  可用于按周汇总 Group by,均支持跨年跨月数据
*/

return
(select --@date,datename(weekday,@date),(@@datefirst + datepart(weekday,@date)) % 7,3 - (@@datefirst + datepart(weekday,@date)) % 7,
           dateadd(day
                  ,case when (@@datefirst + datepart(weekday,@date)) % 7 = 0 --周六
                              then
                                   case when @ between 1 and 6
                                             then @ - 6
                                        else 1
                                    end
                        when (@@datefirst + datepart(weekday,@date)) % 7 = 1 --周日(七)
                              then
                                   case when @ between 1 and 6
                                             then @ - 7
                                        else 0
                                    end

                        when (@@datefirst + datepart(weekday,@date)) % 7 between 2 and 6 --周一至周五
                              then
                                   case when @ between 1 and 6
                                             then  @ + 1 - (@@datefirst + datepart(weekday,@date)) % 7
                                        else 8 - (@@datefirst + datepart(weekday,@date)) % 7
                                   end
                    end
                  ,@date))
/*
测试:

select date,datename(weekday,date),'映射到:',dbo.udf_weekday(2,date),datename(weekday,dbo.udf_weekday(1,date))
from T
order by date

--===============
set datefirst 4
declare @ int,@a int
set @ = 1

select date,datename(weekday,date),(@@datefirst + datepart(weekday,date)) % 7,3 - (@@datefirst + datepart(weekday,date)) % 7,
           dateadd(day
                  ,case when (@@datefirst + datepart(weekday,date)) % 7 = 0 --周六
                              then
                                   case when @ between 2 and 7
                                             then -(7-@)
                                        else @
                                    end
                        when (@@datefirst + datepart(weekday,date)) % 7 = 1 --周日
                              then
                                   case when @ between 2 and 7
                                             then -(7-@)-1
                                        else @ - 1
                                    end

                        when (@@datefirst + datepart(weekday,date)) % 7 between 2 and 6
                              then
                                   case when @ between 2 and 7
                                             then  @ - (@@datefirst + datepart(weekday,date)) % 7
                                        else 8 - (@@datefirst + datepart(weekday,date)) % 7
                                   end

                                  
                    end
                  ,date)
from d
order by date
*/

end