1093 - You can't specify target table 'xxx' for update in FROM clause

MySQL版本：5.7.20
操作表数据结构如下：

一 需求

将下级部门和上级部门关联，更新下级部门的parent_id 字段为上级部门的id字段值，SQL语句如下：

UPDATE department set parent_id= 
(select id from department where department_name = 'dep_1')
where department_level ='2';

报错如下：

[Err] 1093 - You can't specify target table 'department' for update in FROM clause

意思是FROM 条件中不能指定要更新的目标表，看来MySQL并不支持这种子查询方式的更新操作，MySQL手册也对该问题作了说明：
“This error occurs in cases such as the following, which attempts to modify a table and select from the same table in the subquery:
UPDATE t1 SET column2 = (SELECT MAX(column1) FROM t1);”

二 解决方法

将子查询作为临时表，然后选择临时表相关字段作为条件值进行更新。
更新语句如下：

UPDATE department,
 (select id from department where department_name = 'dep_1') temp
set parent_id = temp.id
where department_level ='2';

执行后结果如下：

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参考：MySQL :: MySQL 5.7 Reference Manual :: 13.2.10.9 Subquery Errors