Oracle分页，Oracle中rownum与rowid的理解
select * from tablename where rownum>0
select?? t2.*
from (select rid
????????? from (select r.rid, rownum linenum
????????????????? from (select???????????????????
???????????????????????? rowid rid
????????????????????????? from tablename t
???????????????????????? [条件限制]) r
???????????????? WHERE rownum <= 50)
???????? WHERE linenum >=1) t1,
?????? tablename t2
where t1.rid = t2.rowid（利用rowid分页，效率最高的一种，t2.*根据需要换成需要查询的列）
