SQL查询删除重复值

Question

我有了

Account, CompanyID, Mail_Address 
1001,1,Main ST 
1001,2,Main ST 
1001,3,Florida ST 
1002,1,South Main 
1002,2,West Main 
1002,3,Soth Main 
1003,1,North Main 
1003,2,North Main 

我需要创建一个查询，删除重复MAIL_ADDRESS，这是很容易做到的表。问题是返回的结果是重复值的最后一个，而不是第一个重复的值。

如果我的桌子上面 结果会

Account, CompanyID, Mail_Address 
    1001,2,Main ST 
    1001,3,Florida ST 
    1002,2,West Main 
    1002,3,South Main 
    1003,2,North Main 

通知查询删除第一条记录，并保持最后的重复值的。

我perfer结果是

Account, CompanyID, Mail_Address 
    1001,1,Main ST 
    1001,3,Florida ST 
    1002,1,South Main 
    1002,2,West Main 
    1003,1,North Main 

我的查询

SELECT * 
    FROM (SELECT [ACCOUNT] 
     ,[COMPANY] 
     ,[MAIL_ADDRESS] 
     , 

     ROW_NUMBER() OVER(PARTITION BY Mail_Address ORDER BY Account ASC) rn 
        FROM [SQLUserDB].[dbo].[DSDD01]     

      ) a 
WHERE rn = 1 

Answer 1

如果你是最低的公司的价值后，这将工作：

SELECT Account, MIN(Company) as Company, Mail_Address 
FROM SqlUserDb.dbo.DSDD01 
GROUP BY Account, Mail_Address 

如果你是后第一家上市公司价值，这将做到这一点，非常接近你有：

SELECT Account, Company, Mail_Address 
FROM (
    SELECT Account, Company, Mail_Address, 
    ROW_NUMBER() OVER(PARTITION BY Mail_Address ORDER BY Account, Company) CompanyRowNo 
    FROM SqlUserDb.dbo.DSDD01 
) x 
WHERE x.CompanyRowNo = 1 

Answer 2

只需添加另一个条件到ORDER BY：

SELECT * 
    FROM (SELECT [ACCOUNT] 
     ,[COMPANY] 
     ,[MAIL_ADDRESS] 
     , 

     ROW_NUMBER() OVER(PARTITION BY Mail_Address ORDER BY Account ASC, CompanyID) rn 
        FROM [SQLUserDB].[dbo].[DSDD01]     

      ) a 
WHERE rn = 1 

Answer 3

可以使用not exists实现自己的意图：

select Account, CompanyID, Mail_Address 
FROM [SQLUserDB].[dbo].[DSDD01] t1 
where not exists (select 1 
        from [SQLUserDB].[dbo].[DSDD01] t2 
        where t1.Mail_Address = t2.Mail_Address and t2.CompanyID < t1.CompanyID) 

Answer 4

只是为了显示你的另一种方法，使用表对自身内部联接：

-- List Mail_Address to Delete 
select t1.Account, t1.CompanyID, t1.Mail_Address 
from [SQLUserDB].[dbo].[DSDD01] t1 
inner join [SQLUserDB].[dbo].[DSDD01] t2 
on t1.Account = t2.Account 
and t1.Mail_Address = t2.Mail_Address 
where t1.CompanyID > t2.Company_ID 

-- Delete Duplicate Mail_Address 
delete t1 
from [SQLUserDB].[dbo].[DSDD01] t1 
inner join [SQLUserDB].[dbo].[DSDD01] t2 
on t1.Account = t2.Account 
and t1.Mail_Address = t2.Mail_Address 
where t1.CompanyID > t2.Company_ID