获取一周的第一天 T-SQL

Question

如何获得一周的第一天（星期一），其中周 = 6 年 = 2020 我需要得到 10.02.2020

例如。 2020 年第 1 周的日期为 06.01.2020 - 12.01.2020 2020 年第 6 周的日期为 10.02.2020 - 16.02.2020

Answer 1

DECLARE @YEAR int = 2020;
DECLARE @WEEKSTOADD int = 6;
SET DATEFIRST 1;

SELECT 
        DATEADD(day, 
                1 -  DATEPART(dw,DATEADD(week,@WEEKSTOADD,cast(cast(@YEAR as varchar(4)) + '0101' as date))), 
                DATEADD(week,@WEEKSTOADD,cast(cast(@YEAR as varchar(4)) + '0101' as date)))

Answer 2

无论DateFirst或Language的设置如何，以下代码都将获取给定日期所在周的星期一日期：

Cast( DateAdd( day, - ( @@DateFirst + DatePart( weekday, Datum ) - 2 ) % 7, Datum ) as Date )

示例数据示例：

with SampleData as (
  select GetDate() - 30 as Datum
  union all
  select DateAdd( day, 1, Datum )
    from SampleData
    where Datum < GetDate() )
select Datum,
  -- 1 = Monday through 7 = Sunday.
  ( @@DateFirst + DatePart( weekday, Datum ) - 2 ) % 7 + 1 as WeekDay,
  -- Date of Monday in the week of the supplied date.
  Cast( DateAdd( day, - ( @@DateFirst + DatePart( weekday, Datum ) - 2 ) % 7, Datum ) as Date ) as Monday
  from SampleData;

Answer 3

根据示例数据，您需要substring() ：

select t.*, substring(datnum, charindex(' ', datnum) + 1, 10) as dt
from table t
where t.week = 6;