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  • 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

    1SELECT * 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;
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  • 原文地址:https://www.cnblogs.com/Lightning-Kid/p/3863260.html
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