通過join進行過濾的思路很贊。怕有的同學看不清楚sql，我這里根據記憶重寫一遍：
select a.user_name, b.skill, c.skill
from user1 as a inner join user_skills as b on a.id = b.user_id and b.skill = '念經'
inner join user_skills as c on b.user_id = c.user_id and c.skill = '變化'
where b.skill_level > 0 and c.skill_level > 0;
