用于计算重复项的 SQL 查询 [重复]

Posted 2023-02-24

【中文标题】用于计算重复项的 SQL 查询 [重复]

【英文标题】：SQL query to count duplicates [duplicate]

【发布时间】：2017-10-10 14:59:04

【问题描述】：

请帮助我获取一个查询以计算重复项和一个查询以删除重复项。

【问题讨论】：

提示：查看GROUP BY。

google.co.uk/search?q=sql+query+count+duplicates

你开始查询了吗，你能写什么SQL吗？

阅读***.com/help/how-to-ask。然后添加示例表数据和预期结果 - 以及格式化文本。并向我们​​展示您当前的查询尝试。并标记您正在使用的 dbms！

试试这个 DELETE FROM tblUsers WHERE ID IN (SELECT ID FROM tblUsers GROUP BY name, email HAVING COUNT(*) > 1)

【参考方案1】：

我同意所有的 cmets 所以请看How To Ask

如果这对你有用，并且为了它对我自己来说是一个很好的练习，它可以帮助其他人偶然发现这一点，这里有一些通用代码可以做到这一点：

  WITH CTE AS
  (
    SELECT 
    COALESCE(Col1,'') AS Col1, 
    COALESCE(Col2,'') AS Col2, ROW_NUMBER() OVER(PARTITION BY col1,col2 ORDER BY col1,col2) AS row_id
    FROM MyTable
  )

DELETE CTE WHERE row_id >1;

例子：

Create table #things (FirstName varchar(10), LastName varchar(10))
insert into #things (FirstName, LastName) 
values('thing','lastthing'),('thing','lastthing'),('otherthing', 'something')

select * from #things

  ;WITH CTE AS
  (
    SELECT 
    COALESCE(firstname,'') AS Col1, 
    COALESCE(lastname,'') AS Col2, ROW_NUMBER() OVER(PARTITION BY firstname,lastname ORDER BY firstname,lastname) AS row_id
    FROM #things
  )

DELETE CTE WHERE row_id >1;

select * from #things

drop table #things