MySQL4中嵌套子查询删除出错解决方案

MySQL4中嵌套子查询删除出错解决方案

 

MySQL4中嵌套子查询做删除操作会出错，例如下面的SQL：

delete from moviesparam
where mpeg in ( select mp.mpeg
                                         from movies mv, moviesparam mp
                                     where mv.mpeg = mp.mpeg)

 

执行提示：

 

错误码: 1093
You can't specify target table 'moviesparam' for update in FROM clause

 

原因：所删除表的在子查询中出现，就会出错，当然，此SQL放到MySQL5中执行是没有问题的。

 

为了解决此问题，可以建立一张临时表，将子查询的数据写入到临时表，然后做子查询删除即可。

当然，此处的临时表并被真是真正意义的临时表，是临时创建一个表，用完后再删除。代码如下：

drop table if exists tmp_del_mp;

create table tmp_del_mp as
select mpeg from moviesparam where mpeg not in ( select mpeg from movies);

delete from moviesparam where mpeg in ( select mpeg from tmp_del_mp);

drop table if exists tmp_del_mp;

 

这样就变相的实现了所要实现的功能。

 

将上面的SQL放置到JDBC代码中执行：

Statement stmt = conn.createStatement();    
stmt.addBatch( "drop table if exists tmp_del_mp");    
stmt.addBatch( "create table tmp_del_mp as\n" +    
     "select mpeg from moviesparam where mpeg not in (select mpeg from movies)");    
stmt.addBatch( "delete from moviesparam where mpeg in (select mpeg from tmp_del_mp)");    
stmt.addBatch( "drop table if exists tmp_del_mp");    
stmt.executeBatch();