oracle select limit的方法

选择表中的某一行记录：(理解：rownum是oracle系统顺序分配为从查询返回的行的编号)            select * from (select rownum a,t.* from testtab t) where a=2;            不能为：            select * from (select rownum,t.* from testtab t) where rownum=2;或            select * from testtab where rownum=2;            返回多行记录：            select * from testtab where rownum<=10;            返回某段记录：(如取记录表中4-10行)            select * from (select rownum no,testtab.* from testtab where rownum<=10) where no>=4;            返回有条件且经过排序的某段记录：            select rownum num1,tt.* from             (select rownum num,t.* from             (select EcodeInfo.* from EcodeInfo where a=1 order by ecode desc) t) tt             where num>19 and rownum<20>             以为oracle是先提取记录再排序的，而oracle的rownum是在提取记录就已经生成，它先于排序操作，所以必须使用子查询先排序。            不能为：            select * from tsettab where rownum>10;            返回最后一行记录:            select * from (select rownum a,t.* from testtab t) where a=(select count(*) from testtab);            返回最后N行记录：            select * from (select rownum a,t.* from testtab t) where a=(select count(*)-N from testtab);             ----------------            select * from adminrole where rownum<=4            minus             select * from adminrole where rownum<2>            select * from             (select rownum row_id ,b.* from (select a.* from sorttable a order by sortid)b)             where row_id between 5 and 9;