sql日期操作

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--取得日期所在周的第一天

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SELECT  DATEADD(wk,DATEDIFF(wk,0,getdate()),-1)

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--根据年和周，取得所在周的第一天

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declare @CurWeek nvarchar(10) = '2013_2';
declare @Date datetime;
declare @Week int;
 set @Week = convert(int,substring(@CurWeek,6,2));
declare @Year varchar(4);
 set @Year = left(@CurWeek,4);
 
--当年的第一天
select @Date = dateadd(wk,@Week-1,@Year);
--select dateadd(dd,1-datepart(dw,@Date),@date),dateadd(dd,7-datepart(dw,@Date),@Date)
declare @WeekFstDate varchar(10);
 set @WeekFstDate = convert(varchar(10),dateadd(dd,1-datepart(dw,@Date),@Date),120);
select @WeekFstDate;