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使用mysql在删除表中重复记录
delete from user where username in (select user name form(select username from user group by username having count(username)>1));
遇到mysql报错You can‘t specify target table for update in FROM clause
上网百度了下原来是mysql中不允许先select出同一表中的某些值，再update这个表(在同一语句中)，这个问题只出现于mysql，sqlserver和oracle不会出现此问题
解决办法：将select出的结果再通过中间表select一遍
delete from user where username in (select a.username from(select username from user group by username having count(username)>1)a);
这样delete和select的就不是同一个表了
mysql中You can't specify target table for update in FROM clause
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原文地址：http://www.cnblogs.com/pokid/p/5892030.html
