请教一个sql查询的问题，高手指点，谢谢....

请教一个sql查询的问题，高手指点，谢谢....

1，select username, powername from tbuser u,tbuserrole ur,tbrole r where u.id=ur.user_id and ur.role_id=r.id
用到三张表

2，select username, powername from tbuser u,tbuserrole ur,tbrolepower rp,tbpower p where u.id=ur.user_id and ur.role_id=rp.role_id and rp.power_id=p.id
角色表(tbrole)可以省略过

3，用户角色信息的权限信息一起给你查找出来：
select username,rolename, powername from tbuser u,tbuserrole ur,tbrole,tbrolepower rp,tbpower p where u.id=ur.user_id and ur.role_id=r.id and ur.role_id=rp.role_id and rp.power_id=p.id

同样的问题？都是我回答的没问题把？

select a.username,c.rolename
from tbuser a
left join tbuserrole b
on a.id=b.user_id
left join tbrole c
on b.role_id=c.id
select a.username,e.powername
from tbuser a
left join tbuserrole b
on a.id=b.user_id
left join tbrole c
on b.role_id=c.id
left join tbrolepower d
on c.id=d.role_id
left join tbpower e
on d.power_id=e.id

1、select rolename from tbrole where id=(select role_id from tbuserrole where user_id=(select id from tbuser where username=****))
2、select powername from tbpower where id in（select power_id from tbrolepower where id=(select role_id from tbuserrole where user_id=(select id from tbuser where username=****))）