随机数据库查询

---------------------------随机取一条数据------------------------------------------
select message_name from (select rownum rr,message.* from message)
where rr= (select trunc(dbms_random.value(1,(select count(*) from message)+1)) from dual)
------------------随机排序然后取一条数据-------------------------------------------------------
select a.*,rownum from(select m.* from message m order by dbms_random.random)a where rownum=1