关于Mysql error code 1093

需要做的：一张表里，电话是唯一的，可是有很多重复的记录，现在要做的是 有重复记录的数据，电话号码 全部置为null
重复记录为：843条。

写了很多测试的如下：
1.

update club_member a, (select mobile from club_member group by mobile having count(*) >1) b
set a.mobile='' where a.mobile = b.mobile;

结果：失败，报错：You can't specify target table ‘’
错误提示就是说，不能先select出同一表中的某些值，再update这个表(在同一语句中)
查了下百度和谷歌，说是Mysql的bug,有朋友建议等待mysql升级，哈哈。
2.

update club_member  c set mobile=''  
where  exists (select 1  from club_member a where a.mobile is not null  
group by a.mobile having count(*) >1)

结果：失败，同样的错误
3.

update club_member a, (select mobile from club_member group by mobile having count(*) >1) b
set a.mobile='' where a.mobile = b.mobile;

结果：成功，但是效率超低，重复记录843条，执行了将近5分钟
4.

update club_member  c set mobile='' 
where  exists (select 1  from (select mobile from club_member a where a.mobile is not null
  group by a.mobile having count(*) >1) b  where b.mobile= c.mobile);

结果：成功，执行时间：9.91s

分析：
1、
<code>
select mobile from club_member a where a.mobile is not null
  group by a.mobile having count(*) >1) b
</code>
最里层的子查询，查询出重复记录
2、
<code>
update club_member  c set mobile=''
where  exists (select 1  from (select mobile from club_member a where a.mobile is not null
  group by a.mobile having count(*) >1) b  where b.mobile= c.mobile);
</code>
where b.mobile=c.mobile 是与要修改的自关联表做比较相等
update club_member  c set mobile='' 置为null

最后execute ok
oracle好像可以直接执行1。

Mark here!