Knowing the week of a year, how to find the first and last day of the week?

topfly_ppq

If you know the first week of 2017, how do you find the first and last day of the week?

For example: 2017, the first week, get the following expression
---------------------------------------
2016-12-31 00: 00: 00.000
2017-01-06 00: 00: 00.000


In 2017, the second week, I got the following expression
---------------------------------------
2017-01-07 00: 00: 00.000
2017-01-13 00: 00: 00.000


Eager for advice, thank you

hiqwolfzzh

select top 1 field from (known record set order by field ASC)-the first day
select top 1 field from (known record set order by field DESC)-last day

sinexe

declare @year int,@week int,@day datetime
select @year = 2017,@week = 3,@day = convert(char(4),@year) + '0101'
select dateadd(day,(@week-1)*7 -datepart(week,@day),@day) as the first day, dateadd(day,(@week-1)*7+6-datepart(week,@ day),@day) as the last day

zy_1306

declare @year int, @week int
select @year = 2017, @week = 1
select dateadd(day, @week * 7-datepart(weekday, dateadd(year, @year-1900, 0))-6, dateadd(year, @year-1900, 0)),
       dateadd(day, @week * 7-datepart(weekday, dateadd(year, @year-1900, 0)) + 1, dateadd(year, @year-1900, 0))

wgfxman

From a known first and last day datepart(weekday,,)

topfly_ppq

Thank youzy_1306

sinexesinexewill do, just the first day of the week is Sunday, thank you all

sinexe

Only the first day of the week is Sunday
－－－－－－－－－－－－－
This is it
First day last day
-------------------------------------------------- ---- ---------------------------------------------- --------
2016-12-31 00:00:00.000 2017-01-06 00:00:00.000

(The number of rows affected is 1 row)