Question

我想删除所有重复项，只保留其中一个。

我的查询应该删除所有重复的数据：

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Answer 1

正如Zohar在评论中所述，您的查询将保留 two 重复的行而不是 one ..只保留一行更改您的查询如下..

Check out this question and all its answers有几种方法可以删除像rownumber，group by，self join以及有关何时使用group by vs rownumber的优化提示..

WITH todelete As (
      select em.*,
             row_number() over (partition by emp_num, [from_date],[to_date],[ req_ser], [ req_year]
                                order by (select null)) as cnt
      from empmission em
)

DELETE FROM todelete
WHERE cnt > 1;

Answer 2

首先，我建议您不要使用CTE使用临时表作为您的解决方案使用以下链接找到我为什么这么说

https://dba.stackexchange.com/questions/13112/whats-the-difference-between-a-cte-and-a-temp-table

了解更多使用以下链接

http://www.dotnet-tricks.com/Tutorial/sqlserver/X517150913-Difference-between-CTE-and-Temp-Table-and-Table-Variable.html

现在让我们回到你的解决方案，我使用了Temp Table

Select e.emp_num,e.from_date,e.to_date,e.[ req_ser],e.[ req_year],COUNT(1) number_of_duplicates
into #temp1 from empmission  e
group by emp_num,from_date,to_date,[ req_ser],[ req_year]

Truncate Table empmission 


 Insert into empmission 
 Select t.emp_num,
       t.from_date, 
       t.to_date,
       t.[ req_ser],
       t.[ req_year]
     from #temp1 t
   Drop Table #temp1      --Droping the temp table

  Select * from empmission

或者您可以选择CTE 正如

WITH todelete As (
  select em.*,
         row_number() over (partition by emp_num, [from_date],[to_date],[ req_ser], [ req_year]
                            order by (select null)) as cnt
  from empmission em
  )
  DELETE FROM todelete
WHERE cnt > 1;

如何删除所有重复项只保留其中一个

2 个答案: