SQL Server重复检查

确定SQL Server表中重复记录的最佳方法是什么

例如，我想在表中查找收到的最后一封重复电子邮件（表中有主键、receiveddate和电子邮件字段）

样本数据：

1  01/01/2008 stuff@stuff.com
2  02/01/2008 stuff@stuff.com
3  01/12/2008 noone@stuff.com

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您不能加入电子邮件字段的列表，然后查看结果中的空值吗

或者更好的是，计算每个电子邮件地址的实例？并且只返回计数大于1的值

甚至可以选择电子邮件和id字段。并返回电子邮件相同、ID不同的条目。（为了避免重复，不要使用！=而是）

类似的东西

select email ,max(receiveddate) as MaxDate
from YourTable
group by email 
having count(email) > 1

试试这个

select * from table a, table b
where a.email = b.email

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你想要最后几项的清单吗？如果是这样，您可以使用：

SELECT [info] FROM [table] t WHERE NOT EXISTS (SELECT * FROM [table] tCheck WHERE t.date > tCheck.date)

如果您想要所有重复电子邮件地址的列表，请使用GROUP BY收集类似数据，然后使用HAVING子句确保数量大于1：

SELECT [info] FROM [table] GROUP BY [email] HAVING Count(*) > 1 DESC

如果您想要最后一封重复的电子邮件（单一结果），只需添加“前1名”和“订购人”：

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如果您有代理键，那么使用SQLMenance文章中提到的GROUPBY语法相对容易。本质上，按使两行或多行“相同”的所有字段分组

删除重复记录的示例伪代码

Create table people (ID(PK), Name, Address, DOB)

Delete from people where id not in (
Select min(ID) from people group by name, address, dob
)

尝试以下方法：

SELECT * FROM (
  SELECT *, 
  ROW_NUMBER() OVER (PARTITION BY ReceivedDate, Email ORDER BY ReceivedDate, Email DESC) AS RowNumber 
  FROM EmailTable
) a
WHERE RowNumber = 1

看

Create table people (ID(PK), Name, Address, DOB)

Delete from people where id not in (
Select min(ID) from people group by name, address, dob
)

SELECT * FROM (
  SELECT *, 
  ROW_NUMBER() OVER (PARTITION BY ReceivedDate, Email ORDER BY ReceivedDate, Email DESC) AS RowNumber 
  FROM EmailTable
) a
WHERE RowNumber = 1