选择具有最大列值的行按另一列选择

Question

这应该是一个简单的问题,但我不能让它工作:(

如何选择具有最大列值的行,作为另一列的组？

例如,

我有以下表定义:

ID
Del_Index
docgroupviewid

现在的问题是我想先按结果分组docgroupviewid,然后从每个docgroupviewid组中选择一行,具体取决于哪一行最高del_index.

我试过了

SELECT docgroupviewid, max(del_index),id FROM table
group by docgroupviewid

但是不是以正确的方式回报我id,而是最早id从群体中回归我docgroupviewid.

有任何想法吗？

Answer 1

我自己多次努力,解决方案是以不同的方式思考你的查询.

我想要每个DocGroupViewID行,其中Del_Index是具有该DocGroupViewID的所有行的最高(最大):

SELECT
    T.DocGroupViewID,
    T.Del_Index,
    T.ID
FROM MyTable T
WHERE T.Del_Index = (
    SELECT MAX( T1.Del_Index ) FROM MyTable T1
    WHERE T1.DocGroupViewID = T.DocGroupViewID 
)

当多行可以相同时Del_Index,它会变得更复杂,因为那时你需要一些方法来选择显示哪一行.

编辑:想跟进另一个选项

您可以使用CTE RANK()或ROW_NUMBER()函数来更好地控制结果,如下所示:

-- fake a source table
DECLARE @t TABLE (
    ID int IDENTITY(1,1) PRIMARY KEY,
    Del_Index int,
    DocGroupViewID int
)

INSERT INTO @t
SELECT 1, 1 UNION ALL
SELECT 2, 1 UNION ALL
SELECT 3, 1 UNION ALL
SELECT 1, 2 UNION ALL
SELECT 2, 2 UNION ALL
SELECT 2, 2 UNION ALL
SELECT 1, 3 UNION ALL
SELECT 2, 3 UNION ALL
SELECT 3, 3 UNION ALL
SELECT 4, 3

-- show our source
SELECT * FROM @t

-- select using RANK (can have duplicates)
;WITH cteRank AS
(
    SELECT
        DocGroupViewID,
        Del_Index,
        ID,
        RANK() OVER
            (PARTITION BY DocGroupViewID ORDER BY Del_Index DESC)
        AS RowRank,
        ROW_NUMBER() OVER
            (PARTITION BY DocGroupViewID ORDER BY Del_Index DESC)
        AS RowNumber
    FROM @t
)
SELECT *
FROM cteRank
WHERE RowRank = 1

-- select using ROW_NUMBER
;WITH cteRowNumber AS
(
    SELECT
        DocGroupViewID,
        Del_Index,
        ID,
        RANK() OVER
            (PARTITION BY DocGroupViewID ORDER BY Del_Index DESC)
        AS RowRank,
        ROW_NUMBER() OVER
            (PARTITION BY DocGroupViewID ORDER BY Del_Index DESC)
        AS RowNumber
    FROM @t
)
SELECT *
FROM cteRowNumber
WHERE RowNumber = 1

如果你有办法解决关系,只需将其添加到ORDER BY.