[英]SQL Server query where distinct won't work - to select only unique records - and looking only at one column for uniqueness
[英]How to select unique values looking at only one column in SQL Server?
我使用以下查询(在SQL Server 2008中)从表中获取最后20条记录。
该查询按预期工作,我唯一的问题是这是一个日志表,其中某个itemID
可以出现几次。 有没有办法我只能在这里选择唯一的itemID?
我尝试使用DISTINCT,但这在这里不起作用,因为不是整个行都是重复的,只是itemID可以出现多次(然后时间戳或其他数据不同)。
我的SQL:
ALTER PROCEDURE [dbo].[RC_FetchUpdates]
@departmentID int
AS
BEGIN
SET NOCOUNT ON;
SELECT TOP 20 A.itemID,
A.lastUpdate,
CONVERT(VARCHAR(11), A.modTime, 106) AS modTime,
A.modBy,
B.itemName,
B.linkRef
FROM RC_LogLinks A
LEFT JOIN RC_Links B
ON B.itemID = A.itemID
WHERE B.departmentID = @departmentID
AND A.lastUpdate <> 'Deleted'
ORDER BY A.modTime desc, B.itemName
FOR XML PATH('updates'), ELEMENTS, TYPE, ROOT('ranks')
END
将会是这样的:
WITH rankedLogLinks AS (
SELECT ROW_NUMBER() OVER (PARTITION BY A.itemID ORDER BY A.modTime DESC) AS rownum, A.itemID, A.lastUpdate, A.modTime, A.modBy
FROM RC_LogLinks A
WHERE A.lastUpdate <> 'Deleted'
)
SELECT r.itemID, r.lastUpdate, CONVERT(VARCHAR(11), r.modTime, 106) AS modTime, r.modBy, B.itemName, B.linkRef
FROM rankedLogLinks r
LEFT JOIN RC_Links B
ON B.itemID = r.itemID
WHERE B.departmentID = @departmentID
AND r.rownum = 1
ORDER BY B.itemName
FOR XML PATH('updates'), ELEMENTS, TYPE, ROOT('ranks')
;
您可能需要根据需要将WHERE A.lastUpdate <>“已删除”的位置从第一个查询更改为第二个查询。
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