ORALCE rownum 案例解說

選擇表中的某一行記錄：(理解：rownum是oracle系統順序分配為從查詢返回的行的編號)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;不能為：select * from (select rownum,t.* from testtab t) where rownum=2;或select * from testtab where rownum=2;返回多行記錄：select * from testtab where rownum<=10;返回某段記錄：(如取記錄表中4-10行)select * from (select rownum no,testtab.* from testtab where rownum<=10) where no>=4;返回有條件且經過排序的某段記錄：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> 以為oracle是先提取記錄再排序的，而oracle的rownum是在提取記錄就已經產生，它先於排序操作，所以必須使用子查詢先排序。不能為：select * from tsettab where rownum>10;返回最後一行記錄:select * from (select rownum a,t.* from testtab t) where a=(select count(*) from testtab);返回最後N行記錄：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;