sql script: Calculating Days

--日曆(sql server 2005)

CREATE TABLE T1 (ID INTEGER)
INSERT INTO T1 VALUES (1)
----
with x(dy,dm,mth,dw,wk)
as(
select dy,
       day(dy) dm,
        datepart(m,dy) mth,
       datepart(dw,dy) dw,       
        case when datepart(dw,dy)=1
        then datepart(ww,dy)-1
        else datepart(ww,dy)
        end wk
from(
select dateadd(day,-day(getdate())+1,getdate()) dy
from t1
) x
union all 
select dateadd(d,1,dy),day(dateadd(d,1,dy)),mth,
    datepart(dw,dateadd(d,1,dy)),
    case when datepart(dw,dateadd(d,1,dy))=1
    then datepart(wk,dateadd(d,1,dy))-1
    else datepart(wk,dateadd(d,1,dy))
   end
from x
where datepart(m,dateadd(d,1,dy))=mth
)
select max(case dw when 2 then dm end) as Mo,
       max(case dw when 3 then dm end) as Tu,
       max(case dw when 4 then dm end) as We,
       max(case dw when 5 then dm end) as Th,
       max(case dw when 6 then dm end) as Fr,
       max(case dw when 7 then dm end) as Sa,
       max(case dw when 1 then dm end) as Su
from x
group by wk
order by wk

---
select dy,
        day(dy) dm,
        datepart(m,dy) mth,
        datepart(dw,dy) dw,
        case when datepart(dw,dy)=1
        then datepart(ww,dy)-1
        else datepart(ww,dy)
        end wk
   from(
    select dateadd(day,-day(getdate())+1,getdate()) dy
from t1
) x
go

--第幾周
with x(dy,dm,mth,dw,wk)
as(
select dy,
             day(dy) dm,
        datepart(m,dy) mth,
        datepart(dw,dy) dw,
        case when datepart(dw,dy)=1
        then datepart(ww,dy)-1
        else datepart(ww,dy)
        end wk
from(
select dateadd(day,-day(getdate())+1,getdate()) dy
from t1
) x 
union all 
select dateadd(d,1,dy), day(dateadd(d,1,dy)),mth,
        datepart(dw,dateadd(d,1,dy)),
      case when datepart(dw,dateadd(d,1,dy))=1
         then datepart(wk,dateadd(d,1,dy))-1
         else datepart(wk,dateadd(d,1,dy))
      end
from x
where datepart(m,dateadd(d,1,dy))=mth
)
select * from x

---
CREATE FUNCTION [dbo].[f_week_days_in_period] (@start_date datetime, @end_date datetime)
RETURNS INT
AS
BEGIN
      
      -- If the start date is a weekend, move it foward to the next weekday
      WHILE datepart(weekday, @start_date) in (1,7) -- Sunday, Saturday
      BEGIN
          SET @start_date = dateadd(d,1,@start_date)
      END
      
      -- If the end date is a weekend, move it back to the last weekday
      WHILE datepart(weekday, @end_date) in (1,7) -- Sunday, Saturday
      BEGIN
          SET @end_date = dateadd(d,-1,@end_date)
      END
      
      -- Weekdays are total days in perion minus weekends. (2 days per weekend)
      -- Extra weekend days were trimmed off the period above.
      -- I am adding an extra day to the total to make it inclusive. 
      --     i.e. 1/1/2008 to 1/1/2008 is one day because it includes the 1st
      RETURN (datediff(d,@start_date,@end_date) + 1) - (datediff(ww,@start_date,@end_date) * 2)
  
  END

---
select dbo.f_week_days_in_period('2013-02-01','2013-02-28')