对于表结构

MyTable

RowID int not null identity(1,1) primary key,
Col1 varchar(20) not null,
Col2 varchar(2048) not null,
Col3 tinyint not null

删除重复项的查询:

DELETE t1
FROM MyTable t1
INNER JOIN MyTable t2
WHERE t1.RowID > t2.RowID
  AND t1.Col1 = t2.Col1
  AND t1.Col2=t2.Col2
  AND t1.Col3=t2.Col3;

我假设RowID是一种自动递增，其余列有重复的值。

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

alter table MyTable add sno int identity(1,1)
    delete from MyTable where sno in
    (
    select sno from (
    select *,
    RANK() OVER ( PARTITION BY RowID,Col3 ORDER BY sno DESC )rank
    From MyTable
    )T
    where rank>1
    )

    alter table MyTable 
    drop  column sno

我想提一下这种方法，它可能是有帮助的，并且适用于所有SQL服务器: 通常只有一到两个副本，副本的id和数量是已知的。在这种情况下:

SET ROWCOUNT 1 -- or set to number of rows to be deleted
delete from myTable where RowId = DuplicatedID
SET ROWCOUNT 0

获取重复的行:

SELECT
name, email, COUNT(*)
FROM 
users
GROUP BY
name, email
HAVING COUNT(*) > 1

删除重复的行。

DELETE users 
WHERE rowid NOT IN 
(SELECT MIN(rowid)
FROM users
GROUP BY name, email);      

首先，您可以使用MIN()和Group By选择最小RowId。我们将保留这些行。

   SELECT MIN(RowId) as RowId
   FROM MyTable 
   GROUP BY Col1, Col2, Col3

删除那些不在最小RowId使用范围内的RowId

DELETE FROM MyTable WHERE RowId Not IN()

最后的查询:

DELETE FROM MyTable WHERE RowId Not IN(

    SELECT MIN(RowId) as RowId
    FROM MyTable 
    GROUP BY Col1, Col2, Col3
)

你也可以在SQL Fiddle中检查我的答案