共计 1219 个字符，预计需要花费 4 分钟才能阅读完成。
场景演示：
MySQL> create table test(id int,name varchar(12),primary key(id));
Query OK, 0 rows affected (0.04 sec)
mysql> insert into test values(1,’ttt’);
Query OK, 1 row affected (0.00 sec)
mysql> insert into test values(2,’ttt’);
Query OK, 1 row affected (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> update test set name=’aaaa’ where id in (select id from test);
ERROR 1093 (HY000): You can’t specify target table ‘test’ for update in FROM clause
官方说明：
Error: 1093 SQLSTATE: HY000 (ER_UPDATE_TABLE_USED)
Message: You can’t specify target table ‘%s’ for update in FROM clause
This error occurs for attempts to select from and modify the same table within a single statement. If the select attempt occurs within a derived table, you can avoid this error by setting the derived_merge flag of the optimizer_switch system variable to force the subquery to be materialized into a temporary table, which effectively causes it to be a different table from the one modified. See Section 9.2.2.3,“Optimizing Derived Tables and View References”.
mysql 不支持，在一条语句对同一个表，先查询再更新的操作。
解决方法 1：改成 sql
比如：利用临时表
mysql> update test set name=’aaaa’ where id in (select id from (select id from test)c);
Query OK, 2 rows affected (0.02 sec)
Rows matched: 2 Changed: 2 Warnings: 0
解决方法 2：
官方说：可以通过设置 optimizer_switch 的 derived_merge 参数来解决。
备注：Oracle 是不会这个问题的
本文永久更新链接地址 ：http://www.linuxidc.com/Linux/2017-04/142430.htm
