Oracle Sql学习笔记

select a.tag_id, a.tag_name,b.usernum,b.userscore from tagbase a right join  usertag b on b.tag_id = a.tag_id where rownum <=2 and a.tag_level=2 order by b.usernum desc;select * from tagbase a left outer join  usertag b on a.tag_id = b.tag_id;