如何按特定值计算列？

Question

如何查询这些图片的结果。 第一列选择是本月加上下一列按条件字段（ SelectColumn ）

黄色背景是总和的选择列

我的示例代码。

    declare @myDate date = getdate(),@qry varchar(max)

set @qry = 'select case v.SelectColumn
    when 0 then (SELECT '+DATENAME(month,@myDate)+')
    when 2 then (SELECT '+DATENAME(month,@myDate)+'+'+DATENAME(MONTH,DATEADD(MONTH,1,@myDate))+')
    when 1 then (SELECT '+DATENAME(month,@myDate)+'+'+DATENAME(MONTH,DATEADD(MONTH,1,@myDate))+'+'+DATENAME(MONTH,DATEADD(MONTH,2,@myDate))+')

    end
    as SumColumn

from vwQC12Month v'
exec (@qry)

Answer 1

此问题要求可以将每月值作为行进行访问，以便可以应用选定的聚合。通常，您可以使用UNPIVOT或VALUES将列旋转为行。以下是使用UNPIVOT的工作示例。

在下面的查询中，您必须更改短格式月份名称以匹配您的列名称才能生效。这是一个有效的演示：http://sqlfiddle.com/#!18/094e4/2

另外，您可能想要考虑如何处理年终包装并相应地调整聚合。

-- setup sample data 
create table Test (
  id int, Jan int, Feb int, Mar int, Apr int, May int, 
  Jun int, Jul int, Aug int, Sep int, Oct int, Nov int, Dec int,
  SelectColumn int)

insert Test values
(1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 1),
(2, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 2),
(3, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 3),
(4, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 4)

-- query 
DECLARE @currentMonthNumber int = MONTH(getdate())

-- CTE that rotates the data into rows
; WITH RowsByMonth(id, SelectColumn, monthNumber, val) AS
(
  SELECT id, SelectColumn, CONVERT(int, month) AS monthNumber, val
  FROM
    (SELECT id, SelectColumn, 
       Jan AS [1], Feb AS [2], Mar AS [3], Apr AS [4], 
       May AS [5], Jun AS [6], Jul AS [7], Aug AS [8],
       Sep AS [9], Oct AS [10], Nov AS [11], Dec AS [12] 
     FROM Test) AS Source
     UNPIVOT
     (val FOR month IN 
      ([1], [2], [3], [4],
       [5], [6], [7], [8],
       [9], [10], [11], [12])
     ) AS asRows 
) -- aggregation below 
SELECT id, SUM(val) AS SumAcrossSelectedMonths
FROM RowsByMonth
WHERE 
  monthNumber >= @currentMonthNumber 
  AND monthNumber - @currentMonthNumber < SelectColumn
GROUP BY id

-- Results
| id | SumAcrossSelectedMonths |
|----|-------------------------|
|  1 |                      40 |
|  2 |                      90 |
|  3 |                     150 |
|  4 |                     220 |