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

MySQL版本：5.7.20
操作表數據結構如下：

一 需求

將下級部門和上級部門關聯，更新下級部門的parent_id 字段爲上級部門的id字段值，SQL語句如下：

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

報錯如下：

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

意思是FROM 條件中不能指定要更新的目標表，看來MySQL並不支持這種子查詢方式的更新操作，MySQL手冊也對該問題作了說明：
“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 解決方法

將子查詢作爲臨時表，然後選擇臨時表相關字段作爲條件值進行更新。
更新語句如下：

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

執行後結果如下：

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