八、oracle 分页

oracle的分页一共有三种方式

方法一 根据rowid来分

SELECT *
FROM EMP
WHERE ROWID IN
(SELECT RID
FROM (SELECT ROWNUM RN, RID
FROM (SELECT ROWID RID, EMPNO FROM EMP ORDER BY EMPNO DESC)
WHERE ROWNUM <= ( (currentPage-1) * pageSize + pageSize )) --每页显示几条
WHERE RN > ((currentPage-1) * pageSize) ) --当前页数
ORDER BY EMPNO DESC;

eg、
-- 5 = (currentPage-1) * pageSize + pageSize 每页显示几条
--
0 = (currentPage-1) * pageSize 当前页数
SELECT *
FROM EMP
WHERE ROWID IN
(SELECT RID
FROM (SELECT ROWNUM RN, RID
FROM (SELECT ROWID RID, EMPNO FROM EMP ORDER BY EMPNO DESC)
WHERE ROWNUM <= ( (1-1) * 5 + 5 )) --每页显示几条
WHERE RN > ((1-1) * 5) ) --当前页数
ORDER BY EMPNO DESC;


          

方法二 按分析函数来分

SELECT *
FROM (SELECT T.*, ROW_NUMBER() OVER(ORDER BY empno DESC) RK FROM emp T)
WHERE RK <= ( (currentPage-1) * pageSize + pageSize ) --每页显示几条
AND RK > ( (currentPage-1) * pageSize ); --当前页数


eg、
-- 5 = (currentPage-1) * pageSize + pageSize 每页显示几条
--
0 = (currentPage-1) * pageSize 当前页数
SELECT *
FROM (SELECT T.*, ROW_NUMBER() OVER(ORDER BY empno DESC) RK FROM emp T)
WHERE RK <= 5
AND RK > 0;

               

方法三 按rownum 来分

SELECT *
FROM (SELECT T.*, ROWNUM RN
FROM (SELECT * FROM EMP ORDER BY EMPNO DESC) T
WHERE ROWNUM <= ( (currentPage-1) * pageSize + pageSize )) --每页显示几条
WHERE RN > ( (currentPage-1) * pageSize ); --当前页数

eg、
-- 5 = (currentPage-1) * pageSize + pageSize 每页显示几条
--
0 = (currentPage-1) * pageSize 当前页数
SELECT *
FROM (SELECT T.*, ROWNUM RN
FROM (SELECT * FROM EMP ORDER BY EMPNO DESC) T
WHERE ROWNUM <= 5)
WHERE RN > 0;

其中emp为表名称,empno 为表的主键id,获取按empno降序排序后的第1-5条记录,emp表有70000 多条记录。
个人感觉方法一的效率最好,方法三 次之,方法二 最差。

               

下面通过方法三来分析oracle怎么通过rownum分页的

1
SELECT * FROM emp;
2、显示rownum,由oracle分配的
SELECT e.*, ROWNUM rn FROM (SELECT * FROM emp) e; --rn相当于Oracle分配的行的ID号
3、先查出1-10条记录
正确的: SELECT e.*, ROWNUM rn FROM (SELECT * FROM emp) e WHERE ROWNUM<=10;
错误的:SELECT e.*, ROWNUM rn FROM (SELECT * FROM emp) e WHERE rn<=10;
4、然后查出6-10条记录
SELECT * FROM (SELECT e.*, ROWNUM rn FROM (SELECT * FROM emp) e WHERE ROWNUM<=10) WHERE rn>=6;

 

posted on 2012-02-03 11:05  Ruthless  阅读(8930)  评论(0编辑  收藏  举报