=## oracle使用rownum进行分页语句详解
rownum和rowid是两种不同的东西，不知道你如何利用rowid来分页？
@H_404_6@rownum是返回的记录编号。rowid可理解为返回记录的实际地址。
当根据rowid访问时相当于不经查询直接取数，用rownum必须经过查询（即数据库里有查询动作）。如果已经知道了rowid再去获取数据和通过rownum计数去获取数据，肯定用rowid快。
实际上，由于oracle不支持的真正的分页查询，所谓分页，是先把数据从数据库中查询出来，然后再把对应页的数据返回给调用者，剩余的数据扔掉了。所以，这种情况下，注定用rowid不如用rownum快。
–第一步:
select * from emp;–第二步:
select t1.*,rownum rn from (select * from emp) t1;查询结果如下:rownum为oracle默认的行编号,我们以此来进行分页查询
sql> select t1.*,rownum rn from (select * from emp) t1; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO RN ----- ---------- --------- ----- ----------- --------- --------- ------ ---------- 6666 itguang BOSS 1111 2017/8/1 16 0.00 0.00 40 1 7369 SMITH CLERK 7902 1980/12/17 800.00 20 2 7499 ALLEN SALESMAN 7698 1981/2/20 1600.00 300.00 30 3 7521 WARD SALESMAN 7698 1981/2/22 1250.00 500.00 30 4 7566 JONES MANAGER 7839 1981/4/2 2975.00 20 5 7654 MARTIN SALESMAN 7698 1981/9/28 1250.00 1400.00 30 6 7698 BLAKE MANAGER 7839 1981/5/1 2850.00 30 7 7782 CLARK MANAGER 7839 1981/6/9 2450.00 10 8 7788 SCOTT ANALYST 7566 1987/4/19 8888.00 20 9 7839 KING PRESIDENT 1981/11/17 5000.00 10 10 7844 TURNER SALESMAN 7698 1981/9/8 1500.00 0.00 30 11 7876 ADAMS CLERK 7788 1987/5/23 1100.00 20 12 7900 JAMES CLERK 7698 1981/12/3 950.00 30 13 7902 FORD ANALYST 7566 1981/12/3 3000.00 20 14 7934 MILLER CLERK 7782 1982/1/23 1300.00 10 15– 第三步:查询rownum<=10的数据
select t1.*,rownum rn from (select * from emp) t1 where rownum<=10;查询结果:
sql> select t1.*,rownum rn from (select * from emp) t1 where rownum<=10; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO RN ----- ---------- --------- ----- ----------- --------- --------- ------ ---------- 6666 itguang BOSS 1111 2017/8/1 16 0.00 0.00 40 1 7369 SMITH CLERK 7902 1980/12/17 800.00 20 2 7499 ALLEN SALESMAN 7698 1981/2/20 1600.00 300.00 30 3 7521 WARD SALESMAN 7698 1981/2/22 1250.00 500.00 30 4 7566 JONES MANAGER 7839 1981/4/2 2975.00 20 5 7654 MARTIN SALESMAN 7698 1981/9/28 1250.00 1400.00 30 6 7698 BLAKE MANAGER 7839 1981/5/1 2850.00 30 7 7782 CLARK MANAGER 7839 1981/6/9 2450.00 10 8 7788 SCOTT ANALYST 7566 1987/4/19 8888.00 20 9 7839 KING PRESIDENT 1981/11/17 5000.00 10 10 10 rows selected–第四步:查询5<=rownum<=10之间的数据
select * from (select t1.*,rownum rn from (select * from emp) t1 where rownum<=10) where rn>=5;查询结果
sql> select * from 2 (select t1.*,rownum rn from (select * from emp) t1 where rownum<=10) 3 where rn>=5; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO RN ----- ---------- --------- ----- ----------- --------- --------- ------ ---------- 7566 JONES MANAGER 7839 1981/4/2 2975.00 20 5 7654 MARTIN SALESMAN 7698 1981/9/28 1250.00 1400.00 30 6 7698 BLAKE MANAGER 7839 1981/5/1 2850.00 30 7 7782 CLARK MANAGER 7839 1981/6/9 2450.00 10 8 7788 SCOTT ANALYST 7566 1987/4/19 8888.00 20 9 7839 KING PRESIDENT 1981/11/17 5000.00 10 10 6 rows selected完整oracle分页语句
select * from (select t1.*,rownum rn from (select * from emp) t1 where rownum<=10) where rn>=5;
