SQL语句之计算次数出现最多的值

需求，计算20号部门员工工资出现的次数
使用count() 函数：

SQL> select sal,count(*) time from emp where deptno=20 group by sal;

       SAL   TIME
---------- ----------
      2975      1
      1100      1
      3000      2
       800      1

SQL> 

计算20号部门工资出现的次数，并排出序号
使用dense_rank分析函数

SQL> select sal,dense_rank() over(order by time desc) as seq
  2  from 
  3  (select sal,count(*) time from emp where deptno=20 group by sal) emp;

       SAL    SEQ
---------- ----------
      3000      1
       800      2
      2975      2
      1100      2

SQL> 

根据序号过滤得到序号为2的结果

SQL> select sal
  2  from
  3  (select sal,dense_rank() over(order by time desc) as seq
  4  from
  5  (select sal,count(*) time from emp where deptno=20 group by sal) emp) emp
  6  where seq=2;

       SAL
----------
      2975
       800
      1100

SQL> 

利用partition by 子句分别查询各个部门哪个工资等级的员工多

SQL> select deptno,sal
  2  from
  3  (select deptno,sal,dense_rank() over(partition by deptno order by time desc) as seq
  4  from
  5  (select deptno,sal,count(*) time from emp group by deptno,sal) emp ) emp 
  6  where seq=1;

    DEPTNO    SAL
---------- ----------
    10   5000
    10   1300
    10   2450
    20   3000
    30   1250

SQL> 

以上就是计算次数出现最多的次数的方法。