SQL转换周数到日期（年/月）

Question

I am trying to convert the week number ( for example: 21 ) in SQL-Server to the date (from the Monday of that week) in dd/MM format.

I have searched online but cannot seem to find anything that I could use.

Is this something I can do?

Any help or advice is appreciated.

Thank you in advance.

Answer 1

Try this,

declare @wk int  set @wk = 21
declare @yr int  set @yr = 2016

select dateadd (week, @wk-1, dateadd (year, @yr-1900, 0)) - 4 -
       datepart(dw, dateadd (week, @wk-1, dateadd (year, @yr-1900, 0)) - 4) + 1

or try this way

declare @wk int  = 21

select dateadd(week,@wk-1, DATEADD(wk, DATEDIFF(wk,-1,DATEADD(yy, DATEDIFF(yy,0,getdate()), 0)), 0)) 

Answer 2

You can do it something like:

declare @Week_Number int, @Year int, @Year_Start_Day date, @Week_Day date

select 
    @Week_Number = 1,
    @Year = 2016

select @Year_Start_Day = cast(@Year as nvarchar(4)) + '0101'
select @Week_Day =  dateadd(wk, @Week_Number, @Year_Start_Day)

select dateadd(dd, 1 - datepart(weekday, @Week_Day), @Week_Day)

Answer 3

This will do:

DECLARE @y int = 2016,
        @w int = 21

SELECT CONVERT(nvarchar(5),DATEADD(day,@w*7-(DATEPART(WEEKDAY,CAST(@y as nvarchar(4))+'-01-01')-2),CAST(@y as nvarchar(4))+'-01-01'),3)

Output:

23/05

Answer 4

How about this?

DECLARE @YearNum SMALLINT = 2016;
DECLARE  @WeekNum TINYINT=25;

select 
    SUBSTRING(CONVERT(VARCHAR(10),selected_date,105),0,6) AS WeeKDate
from 
(select DATEADD(dd,t4.i*10000 + t3.i*1000 + t2.i*100 + t1.i*10 + t0.i,'1970-01-01') selected_date from
 (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t0,
 (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t1,
 (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t2,
 (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t3,
 (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t4) v
where YEAR(selected_date)=@YearNum
AND DATEPART(WK,selected_date)=@WeekNum
AND DATEPART(WEEKDAY,selected_date)=2 -- Monday