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mysql Error1093错误

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

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