选择最大值

Question

我想解决一个简单的问题，但我越来越多的细节。

我有2个表，一个有员工，另一个有部门。我的问题：我试图检查哪个部门拥有最多的员工，并仅输出特定的部门。

到目前为止，我有：

select count(*) Number_of_employees 
     from department d, employee e 
     where d.department_id = e.department_id 
     group by department_name 

，输出：

NUMBER_OF_EMPLOYEES  
---------------------- 
2      
4      
3      
3      
3 

我的目标是只输出与这与4名员工的部门雇员最多的部门。

我尝试过使用MAX和JOIN，但是我不太擅长加入，所以我们将不胜感激。

Answer 1

select department_name from 
     (select department_name, count(*) Number_of_employees 
      from department d, employee e 
      where d.department_id = e.department_id 
      group by department_name 
      order by 2 desc) 
    where rownum = 1 

应该做的。

HTH

Answer 2

@Zsolt Botykai

我认为这是正确的，除了由需求为了DESC，我不认为你可以参考number_of_employees查询里面。 （反正你不能在oracle中）。

select department_name 
    from 
    (select department_name 
      ,number_of_employees 
     from 
     (select department_name, count(*) Number_of_employees 
      from department d, employee e 
      where d.department_id = e.department_id 
      group by department_name) 
     order by Number_of_employees DESC) 
    where rownum = 1 

Answer 3

你可以做到这一点，这样既避免了这个rownum：

select 
     max(d.department_name) keep (dense_rank first order by count(1) desc) as department_name 
     , count(1) as number_of_employees 
    from employee e 
    inner join department d on (e.department_id = d.department_id) 
    group by d.department_name 
    ;