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  • 使用Oracle的分析函数ROW_NUMBER、DENSE_RANK、RANK

     

    这三个分析函数都可以在各个分组内从1开始排序。
    ROW_NUMBER()是没有重复值的,可以利用它实现分页显示。
    DENSE_RANK()是连续排序,有两个第二名时仍然跟着第三名。
    RANK()是跳跃排序,有两个第二名时接下来就是第四名(同样是在各个分组内)。

    SELECT * FROM (
         SELECT deptno, ename, sal, ROW_NUMBER()
         OVER (
           PARTITION BY deptno ORDER BY sal DESC
         ) Top3 FROM emp
    )
    WHERE Top3 <= 3

    /

        DEPTNO ENAME                SAL          TOP3
    ---------- ---------- ---------- ----------
               10 KING                   5000             1
               10 CLARK               2450             2
               10 MILLER              1300             3

               20 SCOTT               3000             1
               20 FORD                 3000             2
               20 JONES                2975             3

               30 BLAKE               2850             1
               30 ALLEN               1600             2
               30 TURNER            1500             3

    9 rows selected.

     

    SELECT * FROM (
         SELECT deptno, ename, sal, DENSE_RANK()
         OVER (
           PARTITION BY deptno ORDER BY sal DESC
         ) TopN FROM emp
    )
    WHERE TopN <= 3
    ORDER BY deptno, sal DESC
    /


           DEPTNO ENAME                SAL          TOPN
    ---------- ---------- ---------- ----------
               10 KING                  5000             1
               10 CLARK               2450             2
               10 MILLER              1300             3

           
       20 SCOTT               3000             1     <--- !
              20 FORD                3000             1     <--- !

               20 JONES               2975             2
               20 ADAMS              1100             3

               30 BLAKE               2850             1
               30 ALLEN               1600             2
               30 TURNER            1500             3


    10 rows selected.

     

    SELECT * FROM (
         SELECT deptno, ename, sal, RANK()
         OVER (
           PARTITION BY deptno ORDER BY sal DESC
         ) TopN FROM emp
    )
    WHERE TopN <= 3
    ORDER BY deptno, sal DESC
    /


           DEPTNO ENAME                SAL          TOPN
    ---------- ---------- ---------- ----------
               10 KING                   5000             1
               10 CLARK               2450             2
               10 MILLER              1300             3

           
       20 SCOTT               3000            1     <--- !
              20 FORD                 3000           1     <--- !

               20 JONES               2975            3

               30 BLAKE               2850             1
               30 ALLEN               1600             2
               30 TURNER            1500             3

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  • 原文地址:https://www.cnblogs.com/happyday56/p/795832.html
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