Delete Duplicate Emails
Write a SQL query to delete all duplicate email entries in a table named Person, keeping only unique emails based on its smallest Id. +----+------------------+ | Id | Email | +----+------------------+ | 1 | john@example.com | | 2 | bob@example.com | | 3 | john@example.com | +----+------------------+ Id is the primary key column for this table. For example, after running your query, the above Person table should have the following rows: +----+------------------+ | Id | Email | +----+------------------+ | 1 | john@example.com | | 2 | bob@example.com | +----+------------------+ 先查找,再删除 delete from Person where (id,Email) not in (select id,email from Person group by Email order by Email); ERROR 1093 (HY000): You can't specify target table 'Person' for update in FROM clause 意思是:不能在一个表中查询到删除条件,然后又在这个表里删除进行更新。 解决方法: 创造临时表,然后找到删除条件,最后进行删除更新 select * FROM Person p1 INNER JOIN Person p2 WHERE p1.Email = p2.Email AND p1.Id > p2.Id; +------+---------+------+---------+ | id | Email | id | Email | +------+---------+------+---------+ | 3 | a@b.com | 1 | a@b.com | | 6 | a@b.com | 1 | a@b.com | | 4 | c@d.com | 2 | c@d.com | | 6 | a@b.com | 3 | a@b.com | +------+---------+------+---------+ delete p1 from Person p1 inner join Person p2 where p1.email = p2.email and p1.id > p2.id; 或者 delete p1 from p1 using Person p1 inner join Person p2 where p1.email = p2.email and p1.id > p2.id; [mysql delete多表关联删除](http://blog.csdn.net/havedream_one/article/details/45421017)
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