mysql报错 ERROR 1093 (HY000): You can't specify target table 'a' for update in FROM clause

今天网站有些数据出现异常，需要把出现异常的数据更正，具体操作是把一个表中的publish_date字段关联更新成同一个表中的up_date字段,我们的数据是先存到oracle，然后通过到mysql中的，所有异常数据存在于oracle和mysql。

首先在oracle中更正：

SQL>update infoservice.t_publish_zbxx a set a.publish_date=(select b.up_date from infoservice.t_publish_zbxx b where a.record_id=b.record_id) where a.publish_date>to_date('2017-10-15','yyyy-mm-dd')；

然后对应着改写成mysql相应表和相应sql,居然报错。。。。

mysql> update v_publish_info a set a.publish_date=(select b.up_date from v_publish_info b where a.id=b.id) where a.publish_date>'2017-07-15';

ERROR 1093 (HY000): You can't specify target table 'a' for update in FROM clause

解决办法：

mysql> update v_publish_info a，v_publish_info b set a.publish_date=b.up_date where a.id=b.id and a.publish_date>'2017-07-15';

或者

1，把要更新的几列数据查询出来做为一个第三方表，然后筛选更新。

2，新建一个临时表保存查询出的数据，然后筛选更新。最后删除临时表。

具体如下：

create table liuwenhe.publish_date_temp as select id ,publish_date,up_date from info.v_publish_infowhere publish_date>'2017-07-15';

update info.v_publish_info a set a.publish_date=(select b.up_date from liuwenhe.publish_date_temp b where a.id=b.id) where a.publish_date>'2017-07-15';

为了防止匹配不上，更新为空的问题，可以加上exists条件；

update info.v_publish_info a set a.publish_date=(select b.up_date from liuwenhe.publish_date_temp b where a.id=b.id) where a.publish_date>'2017-07-15' and exists (select b.up_date from liuwenhe.publish_date_temp b where a.id=b.id);

如下是关于关联更新的一些实验：

mysql：

1.成功

mysql> update liuwenhe.publish_date_20170715 a set a.publish_date=(select b.up_date from info.v_publish_info b where a.id=b.id) where a.publish_date>'2017-07-15' and exists (select b.up_date from info.v_publish_info b where a.id=b.id );

Query OK, 0 rows affected (0.00 sec)

Rows matched: 0 Changed: 0 Warnings: 0

2.失败

mysql> update liuwenhe.publish_date_20170715 a set a.publish_date=(select b.up_date from liuwenhe.publish_date_20170715 b where a.id=b.id) where a.publish_date>'2017-07-15';

ERROR 1093 (HY000): You can't specify target table 'a' for update in FROM clause

3.成功

mysql> update liuwenhe.publish_date_20170715 a,liuwenhe.publish_date_20170715 b set a.publish_date=b.in_date where a.id=b.id and a.publish_date>'2017-07-15';

Query OK, 0 rows affected (0.01 sec)

Rows matched: 0 Changed: 0 Warnings: 0

oracle：

4.失败

SQL> update liuwenhe.top_80 a,infoservice.t_member_info b set a.login_id=b.login_id where a.member_id=b.record_id;

update liuwenhe.top_80 a,infoservice.t_member_info b set a.login_id=b.login_id where a.member_id=b.record_id

ERROR at line 1:

ORA-00971: missing SET keyword

5.失败：

SQL> update liuwenhe.top_80 a,liuwenhe.top_80 b set a.login_id=b.login_id where a.member_id=b.member_id;

update liuwenhe.top_80 a,liuwenhe.top_80 b set a.login_id=b.login_id where a.member_id=b.member_id

ERROR at line 1:

ORA-00971: missing SET keyword

6.成功

SQL>update liuwenhe.top_80 a set a.login_id=(select b.login_id from infoservice.t_member_info b where a.member_id=b.record_id);

通过实验1和2比较可以知道，mysql中是不能关联更新同一个表的，但是oracle中可以；实验4和5可以知道oracle中不能使用update a,b set a.=b.之类的语句；实验3可以知道，mysql可以使用update a,b set a.=b.之类的语句来关联更新表；