取后4条纪录
select * from a (
SELECT duty_id, duty_Ftime, duty_Ltime, duty_man
FROM on_duty ORDER by to_number(duty_id) desc
) where rownum <5
select * from a (
SELECT duty_id, duty_Ftime, duty_Ltime, duty_man
FROM on_duty ORDER by to_number(duty_id) desc
) where rownum <5
SELECT duty_id, duty_Ftime, duty_Ltime, duty_man
FROM on_duty ORDER by to_number(duty_id) desc
) a where rownum <5
关于排序和rownum的关系
你的语句是先去取4条,然后进行了排序
而楼上的那个子查询的目的就是先排序,然后去取4条
就是这样的区别,建议看看书,在机械工业出版社有很多经典的书。
FROM on_duty ORDER by to_number(duty_id) desc) where rownum <5;
disconnect;
connect system/manager@.....;
create table aaa as select * from scott.emp;
commit;
select * from aaa order by EMPNO asc
select * from (select * from aaa order by EMPNO asc) a where rownum<5; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- ---------- ---------- ---------- ----------
7369 SMITH CLERK 7902 17-12月-80 800 20
7499 ALLEN SALESMAN 7698 20-2月 -81 1600 300 30
7521 WARD SALESMAN 7698 22-2月 -81 1250 500 30
7566 JONES MANAGER 7839 02-4月 -81 2975 20
7654 MARTIN SALESMAN 7698 28-9月 -81 1250 1400 30
7698 BLAKE MANAGER 7839 01-5月 -81 2850 30
7782 CLARK MANAGER 7839 09-6月 -81 2450 10
7788 SCOTT ANALYST 7566 19-4月 -87 3000 20
7839 KING PRESIDENT 17-11月-81 5000 10
7844 TURNER SALESMAN 7698 08-9月 -81 1500 0 30
7876 ADAMS CLERK 7788 23-5月 -87 1100 20
7900 JAMES CLERK 7698 03-12月-81 950 30
7902 FORD ANALYST 7566 03-12月-81 3000 20
7934 MILLER CLERK 7782 23-1月 -82 1300 10已选择14行。已用时间: 00: 00: 00.16 EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- ---------- ---------- ---------- ----------
7369 SMITH CLERK 7902 17-12月-80 800 20
7499 ALLEN SALESMAN 7698 20-2月 -81 1600 300 30
7521 WARD SALESMAN 7698 22-2月 -81 1250 500 30
7566 JONES MANAGER 7839 02-4月 -81 2975 20已用时间: 00: 00: 00.00