如何从mysql中的表中删除重复的行-数据库问题

how to delete duplicate rows from a table in mysql(如何从mysql中的表中删除重复的行)

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问题描述

我需要从mysql的表中删除重复的记录.所以我有一个表名员工"字段是 empid、empname、empssn

I need to delete duplicate record from table in mysql. So i have a table name "employee" fields are empid, empname, empssn

为了获得重复记录，我写了一个查询

for getting duplicate record i have written a query

     SELECT COUNT(empssn), empssn 
       FROM employee 
GROUP BY empssn 
    HAVING COUNT(empssn)>1

现在我想删除重复的记录.为此我写了查询是.

Now i want to delete duplicate records. for that i have written query is.

DELETE FROM employee 
          WHERE (empid, empssn) NOT IN (SELECT MIN(empid), empssn 
                                                           FROM employee 
                                                    GROUP BY empssn);

你可以假设表中的记录是

you can assume records in table are

EmpId  EmpName  EmpSSN
 -------------------------------
 1  Jack      555-55-5555
 2  Joe      555-56-5555
 3  Fred      555-57-5555
 4  Mike      555-58-5555
 5  Cathy      555-59-5555
 6  Lisa      555-70-5555
 7  Jack      555-55-5555
 8  Mike      555-58-5555
 9  Cathy      555-59-5555
10  Lisa      555-70-5555
11  Lisa      555-70-5555

但我有一个mysql错误是

but i have a mysql error is

不能在 FROM 子句中指定目标表 'employee' 进行更新

You can't specify target table 'employee' for update in FROM clause

推荐答案

将其包装到派生表中的技巧是否适用于这种情况?(基于 http://www.xaprb.com/blog/2006/06/23/how-to-select-from-an-update-target-in-mysql/)

Does the trick of wrapping it into a derived table work for this case? (Based on http://www.xaprb.com/blog/2006/06/23/how-to-select-from-an-update-target-in-mysql/)

DELETE FROM employee WHERE (empid, empssn) NOT IN 
(
SELECT  empid, empssn FROM
(
SELECT MIN(empid) AS empid, empssn FROM employee GROUP BY empssn
) X
);

编辑是的，它似乎可以做到这一点.

Edit Yep it seems to work this end.

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