在使用SQL Server的情况下，如何使用星期数获取星期的开始日期和结束日期？

Question

我已经找到要获取的星期数，但是以不同的方式显示了日期。

实际上，当我检查星期几作为“日期”时

select datepart(wk,'2016-01-02')  //Saturday

output: 1

select datepart(wk,'2016-01-03')  //Sunday

output: 2

但是，当我使用星期数获取星期几的开始日期和结束日期时，它显示出不同的结果。

DECLARE @weekStart INT
DECLARE @weekEnd INT
DECLARE @Year INT

set @weekStart = 1
set @Year = 2016

DECLARE @WeekStartDate date
DECLARE @WeekEndDate date

SET @WeekStartDate = convert(date,DATEADD (WEEK, @weekStart, DATEADD (YEAR, @Year-1900, 0)) - 4 -
                                                DATEPART(DW, DATEADD (WEEK, @weekStart, DATEADD (YEAR, @Year-1900, 0)) - 4) + 1)
SET @WeekEndDate =convert(date,DATEADD (WEEK, @weekStart+1, DATEADD (YEAR, @Year-1900, 0)) - 4 -
                                                DATEPART(DW, DATEADD (WEEK, @weekStart+1, DATEADD (YEAR, @Year-1900, 0)) - 4) + 1)

select @WeekStartDate,@WeekEndDate


output: 
  StartingDate    EndingDate
  --------------------------
  2016-01-03      2016-01-09

我期望输出为，如果我给周= 1，则应该给定StartingDate = ** 2016-01-01和** EndingDate = 2016-01-02

对于第2周，应该给出2016-01-03 2016-01-09

Answer 1

您可以获取本周的绝对开始/结束时间，然后根据当前年份调整第一周的开始时间和最后一周的结束时间。 您实际上只需要计算开始时间，因为结束时间是开始+ 6天：

create procedure spWeekDates @year int, @week int
as
declare @firstWeekDay int
declare @yearStart datetime, @weekStartDate datetime, @weekEndDate datetime

set datefirst 7 -- change as needed
set @yearStart=cast(@year as char(4))+'0101' -- years always start on 01/01 [citation needed]
set @firstWeekDay=datepart(weekday,@yearStart)

-- absolute start/end dates
set @weekStartDate=dateadd(week,@week-1,@yearStart)-@firstWeekDay+1
set @weekEndDate=dateadd(day,6,@weekStartDate)
-- adjusting for target year
if year(@weekStartDate)<@year set @weekStartDate=@yearStart
if year(@weekEndDate)>@year set @weekEndDate=cast(@year as char(4))+'1231'

select @weekStartDate as WeekStartDate, @weekEndDate as WeekEndDate
go

exec spWeekDates 2016,1
exec spWeekDates 2016,2
exec spWeekDates 2016,53
go

结果：

|       WeekStartDate |         WeekEndDate |
|---------------------|---------------------|
| 2016-01-01 00:00:00 | 2016-01-02 00:00:00 |

|       WeekStartDate |         WeekEndDate |
|---------------------|---------------------|
| 2016-01-03 00:00:00 | 2016-01-09 00:00:00 |

|       WeekStartDate |         WeekEndDate |
|---------------------|---------------------|
| 2016-12-25 00:00:00 | 2016-12-31 00:00:00 |

Answer 2

您必须获得一年中第一天的星期几
如果不等于1，则必须set @weekStart = @weekStart -1
并set @StartingDate = first day in year