我更喜欢CTE从sql server表中删除重复的行

强烈推荐阅读本文::http://codaffection.com/sql-server-article/delete-duplicate-rows-in-sql-server/

保持原创性

WITH CTE AS
(
SELECT *,ROW_NUMBER() OVER (PARTITION BY col1,col2,col3 ORDER BY col1,col2,col3) AS RN
FROM MyTable
)

DELETE FROM CTE WHERE RN<>1

不保留原创

WITH CTE AS
(SELECT *,R=RANK() OVER (ORDER BY col1,col2,col3)
FROM MyTable)
 
DELETE CTE
WHERE R IN (SELECT R FROM CTE GROUP BY R HAVING COUNT(*)>1)

在微软支持网站上有一篇关于删除重复文件的好文章。这是相当保守的——他们让你在不同的步骤中做所有的事情——但它应该适用于大的表格。

在过去，我使用了自连接来实现这一点，尽管它可能会用一个HAVING子句来美化:

DELETE dupes
FROM MyTable dupes, MyTable fullTable
WHERE dupes.dupField = fullTable.dupField 
AND dupes.secondDupField = fullTable.secondDupField 
AND dupes.uniqueField > fullTable.uniqueField

通过使用下面的查询，我们可以基于单列或多列删除重复的记录。下面的查询是基于两列进行删除。表名为:testing，列名为empno,empname

DELETE FROM testing WHERE empno not IN (SELECT empno FROM (SELECT empno, ROW_NUMBER() OVER (PARTITION BY empno ORDER BY empno) 
AS [ItemNumber] FROM testing) a WHERE ItemNumber > 1)
or empname not in
(select empname from (select empname,row_number() over(PARTITION BY empno ORDER BY empno) 
AS [ItemNumber] FROM testing) a WHERE ItemNumber > 1)

如果您想预览要删除的行，并控制要保留的重复行。参见http://developer.azurewebsites.net/2014/09/better-sql-group-by-find-duplicate-data/

with MYCTE as (
  SELECT ROW_NUMBER() OVER (
    PARTITION BY DuplicateKey1
                ,DuplicateKey2 -- optional
    ORDER BY CreatedAt -- the first row among duplicates will be kept, other rows will be removed
  ) RN
  FROM MyTable
)
DELETE FROM MYCTE
WHERE RN > 1

另一种表达方式:——

DELETE A
FROM   TABLE A,
       TABLE B
WHERE  A.COL1 = B.COL1
       AND A.COL2 = B.COL2
       AND A.UNIQUEFIELD > B.UNIQUEFIELD 

假设没有空值，您GROUP BY唯一的列，并选择最小(或最大)RowId作为要保留的行。然后，删除所有没有行id的内容:

DELETE FROM MyTable
LEFT OUTER JOIN (
   SELECT MIN(RowId) as RowId, Col1, Col2, Col3 
   FROM MyTable 
   GROUP BY Col1, Col2, Col3
) as KeepRows ON
   MyTable.RowId = KeepRows.RowId
WHERE
   KeepRows.RowId IS NULL

如果您使用的是GUID而不是整数，则可以进行替换

MIN(RowId)

with

CONVERT(uniqueidentifier, MIN(CONVERT(char(36), MyGuidColumn)))