根据分组依据删除重复项 - SQL

Question

编辑：我想我现在有了解决方案，但需要做更多的意义检查...

DELETE TBLFIRE_TEMP3 FROM TBLFIRE_TEMP3
LEFT OUTER JOIN (
   SELECT MIN(FireNo) as FireNo, ActionRef, FRADate, FIREUPRN
   FROM TBLFIRE_TEMP3 
   GROUP BY ActionRef, FRADate, FIREUPRN
) as KeepRows ON
   TBLFIRE_TEMP3.FireNo = KeepRows.FireNo
WHERE
   KeepRows.FireNo IS NULL

-############### 之前的评论###############

我有一个 table 其中有重复项（基于三列）。我可以通过执行以下操作找到它们并查看它们，然后只想删除重复项（即所有计数（*）结果都是“1”）

SELECT COUNT(*),ActionRef, FRADate, FIREUPRN
FROM TBLTempTable
GROUP BY ActionRef, FRADate, FIREUPRN

所以我可以看到这些组出现的次数。我想要做的是删除重复项。我试过下面的但它删除了每一行，甚至单数：

DELETE a FROM TblTempTable a JOIN
(
  SELECT ActionRef, FRADate, FIREUPRN
    FROM TblTempTable 
   GROUP BY ActionRef, FRADate, FIREUPRN
) d 
   ON (a.ActionRef = b.ActionRef
  AND a.FRADate = b.FRADate
AND a.FIREUPRN = b.FIREUPRN)

根据我查看指南的代码，我相信我已经接近了，但目前它删除了所有内容。

参考资料： SQL- How can I remove duplicate rows? GROUP BY does not remove duplicates

-这些是 MySQL 所以最后不相关：

select and delete rows within groups using mysql Find duplicate records in MySQL

Answer 1

一个简单的解决方案是使用 CTE ROW_NUMBER:

WITH Data AS
(
    SELECT RN  = ROW_NUMBER() OVER (PARTITION BY ActionRef, FRADate, FIREUPRN
                                    ORDER BY FRADate ASC),
           Cnt = COUNT(*) OVER (PARTITION BY ActionRef, FRADate, FIREUPRN),
           ActionRef, FRADate, FIREUPRN
    FROM TBLTempTable
)
DELETE FROM Data
WHERE RN > 1

这会删除除一个以外的所有内容，它会保留最旧的 FRADate。您需要更改 ROW_NUMBER 中的 ORDER BY 才能更改此逻辑。

CTE 的一个优点是您可以轻松更改它以查看要删除（或更新）的内容。因此，您只需将 DELETE FROM Data 替换为 SELECT * FROM Data.

Answer 2

还有一个更简单的可读性方法：

;WITH DEDUPE AS (
SELECT ROW_NUMBER() OVER(
    PARTITION BY ActionRef, FRADate, FIREUPRN
        ORDER BY (SELECT 1)) AS RN
FROM TBLTempTable)
DELETE FROM DEDUPE
WHERE RN != 1

我们每天都在工作中使用这个确切的脚本。如果您想根据日期列等保留较新的行，则可以将 ORDER BY 子句更改为任何列。

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