欧洲标准周和年分组问题

Question

有一个日期部分 iso_week 返回选定日期的 iso_week。

SELECT DATEPART(iso_week, getdate())

这将返回周电流的欧洲标准。它不一定和星期一样。

棘手的部分来了：

SELECT DATEPART(iso_week, '2011-01-01')

返回

52 

所以它属于去年 为了按年和 iso_week 分组，我需要考虑 iso_week 不是来自同一年。

Iso_week 从星期一开始，属于大多数日子重叠的年份。所以 2010 年有 4 天，2011 年有 3 天，一周是 52 天，所有天都属于 iso_year 2010。但是 TSQL 没有 detepart iso_year。

declare @t table(col1 datetime)

insert @t 
ALL SELECT '2010-12-28'
UNION ALL SELECT '2010-12-29'
UNION ALL SELECT '2010-12-30'
UNION ALL SELECT '2010-12-31'
UNION ALL SELECT '2011-01-01'
UNION ALL SELECT '2011-01-02'
--UNION ALL SELECT '2011-01-03' Stackexchange is bugged and can't handle this line showing 53
UNION ALL SELECT '2011-01-04'

我需要类似的东西（iso_year 不存在）：

SELECT DATEPART(ISO_WEEK, col1) WEEK, DATEPART(iso_YEAR, col1) YEAR, COUNT(*) COUNT 
FROM @t
GROUP BY DATEPART(ISO_WEEK, col1), DATEPART(iso_YEAR, col1)
ORDER BY  2,1

预期结果

WEEK  YEAR          COUNT
52    2010           6
1     2011           2

Answer 1

同一 ISO 周的星期四将明确地为您提供正确的年份。并且this answer 可以为您提供如何从给定日期获得正确的星期四的想法。

SELECT
  Week  = DATEPART(ISOWK, TheThursday),
  Year  = DATEPART(YEAR, TheThursday),
  Count = COUNT(*)
FROM (
  SELECT
    TheThursday = DATEADD(
      DAY,
      3 - (DATEPART(DW, col1) + @@DATEFIRST - 2) % 7,
      col1
    )
  FROM @t
) s
GROUP BY
  TheThursday

Answer 2

您可以检查 dayofyear 和 iso_week 以确定是否需要用 1 减去年份。

select datepart(iso_week, col1) as [week], 
       case when datepart(dayofyear, col1) < 7 and
                 datepart(iso_week, col1) > 51
            then year(col1) - 1
            else year(col1)
       end as [year], 
       count(*) as [count]
from @t
group by datepart(iso_week, col1),
         case when datepart(dayofyear, col1) < 7 and
                   datepart(iso_week, col1) > 51
              then year(col1) - 1
              else year(col1)
         end
order by [year], [week]

Answer 3

已编辑...

SELECT 
  IsoWeek  = DATEPART(ISO_WEEK, TheDate), 
  IsoYear  = CASE 
    WHEN 
      MONTH(TheDate) = 1 AND DATEPART(ISO_WEEK, TheDate) > 51 
      THEN YEAR(TheDate) - 1 
      ELSE YEAR(TheDate) 
    END, 
  DayCount = COUNT(*)
FROM 
  @t
GROUP BY 
  DATEPART(ISO_WEEK, TheDate), 
  CASE 
    WHEN MONTH(TheDate) = 1 AND DATEPART(ISO_WEEK, TheDate) > 51 
    THEN YEAR(TheDate) - 1 
    ELSE YEAR(TheDate) 
  END 
ORDER BY  
  IsoYear,
  IsoWeek

--IsoWeek  IsoYear  DayCount
--     52     2010         6
--      1     2011         2

Answer 4

此解决方案还可以处理一周从前一年开始的年份。

SELECT DATEPART(ISO_WEEK, col1) WEEK, 
DATEPART(year , col1 - CAST(col1-.5 as int)%7 + 3) YEAR, 
COUNT(*) COUNT 
FROM @t
GROUP BY DATEPART(ISO_WEEK, col1), 
DATEPART(year , col1 - CAST(col1-.5 as int)%7 + 3)
ORDER BY 2,1