Error Code: 1093. You can't specify target table 'xxx' for update in FROM clause.
意思大概是：MySql不支持在Update语句中引用被update对象。
原SQL如下：
update sec_menu_item as m
set
m.code = (
select
concat(CONCAT(pinyin(mp.title), '_'),
pinyin(m.title))
from
sec_menu_item as mp
where
mp.id = m.parent_id
);
报上述错误，改动后如下：
update sec_menu_item as m inner join (
select mp.id,mp.title from
sec_menu_item as mp
) as tmp on m.parent_id = tmp.id
set m.code=concat(concat(pinyin(tmp.title),'-'),pinyin(m.title));
执行通过。