用于删除重复值的 SQL 查询答案

【问题标题】：SQL Query for removing duplicate values用于删除重复值的 SQL 查询
【发布时间】：2017-03-22 19:59:26
【问题描述】：

我有一张桌子

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

我需要创建一个删除重复 Mail_Address 的查询，这很简单。问题是返回的结果是最后一个重复值，而不是第一个重复值。

如果我的桌子是上面的结果将是

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

请注意，查询删除了第一条记录并保留了最后一条重复值。

我希望结果是这样的

 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

【问题讨论】：

标签： sql

【解决方案1】：

只需在ORDER BY 中添加另一个条件：

 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

【讨论】：

【解决方案2】：

如果您追求最低的公司价值，这将起作用：

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

如果您追求的是首次上市的公司价值，这将做到，非常接近您所拥有的：

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

【讨论】：

【解决方案3】：

您可以使用not exists实现您的意图：

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)

【讨论】：

【解决方案4】：

只是向您展示另一种方式，在自身上使用 table 的内部连接：

-- 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

【讨论】：