Oracle 中rownum的用法

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;
select * from (select rownum a,t.* from testtab t) where a=3;
select * from (select rownum a,t.* from testtab t) where a=4;

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,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 

返回最后一行记录:

select * from (select rownum a,t.* from testtab t) where a=(select count(*) from testtab);

返回最后第N行记录：

select * from (select rownum a,t.* from testtab t) where a=(select count(*)-N from testtab); 

分页

select tt.num,tt.* from 
(select t.*,rownum num from (select * from infotable a where a = 10 order by a.id) t where rownum <= 20) tt where tt.num>10

不能使用
select a.* from table a where a.rownum <10;
要直接使用
select a.* from table a where rownum <10;