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[英]MySQL - Select rows where column value is only 0, group by another column?
[英]Select Rows with Maximum Column Value group by Another Column
這應該是一個簡單的問題,但我不能讓它工作:(
如何選擇具有最大列值的行,作為另一列的組?
例如,
我有以下表定義:
ID
Del_Index
docgroupviewid
現在的問題是我想docgroupviewid
按結果docgroupviewid
,然后從每個docgroupviewid
組中選擇一行,具體取決於哪一行具有最高的del_index
。
我試過了
SELECT docgroupviewid, max(del_index),id FROM table
group by docgroupviewid
但是不是使用正確的id
返回給我,而是返回具有相同docgroupviewid
的組中最早的id
。
有任何想法嗎?
我自己多次努力,解決方案是以不同的方式思考你的查詢。
我想要每個DocGroupViewID行,其中Del_Index是具有該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
)
當多個行可以具有相同的Del_Index
,它會變得更復雜,因為那時您需要某種方式來選擇要顯示的行。
您可以將RANK()
或ROW_NUMBER()
函數與CTE一起使用,以獲得對結果的更多控制,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
如果您有辦法解決關系,只需將其添加到ORDER BY
。
您將不得不稍微復雜一下您的查詢:
select a.docgroupviewid, a.del_index, a.id from table a
where a.del_index = (select max(b.del_index) from table
where b.docgroupviewid = a.docgroupviewid)
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