You can't specify target table 'XXX' for update in FROM clause

报错如题，意思大致是：在一条 sql 语句中不能先查出来部分内容，再同时又对当前表作修改。
解决方法：给查询加别名，用中间表来实现不是对同一表作操作。

如错误定法：

UPDATE appbricks_department
SET rank = '2'  
WHERE parent_id in (SELECT id FROM appbricks_department WHERE parent_id IS NULL) ;

改后的写法：

UPDATE appbricks_department
SET rank = '2'  
WHERE parent_id in
 (SELECT * FROM (SELECT id FROM appbricks_department WHERE parent_id IS NULL) a );