八、oracle 分页

oracle的分页一共有三种方式

方法一 根据rowid

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

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  rownum

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;

感觉方法一的效率最好，方法三 次之，方法二 最差。