選擇最大值

Question

我想解決一個簡單的問題，但我越來越多的細節。

我有2個表，一個有員工，另一個有部門。我的問題：我試圖檢查哪個部門擁有最多的員工，並僅輸出特定的部門。

到目前爲止，我有：

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

，輸出：

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

我的目標是隻輸出與這與4名員工的部門僱員最多的部門。

我嘗試過使用MAX和JOIN，但是我不太擅長加入，所以我們將不勝感激。

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 

應該做的。

HTH

Answer 2

@Zsolt Botykai

我認爲這是正確的，除了由需求爲了DESC，我不認爲你可以參考number_of_employees查詢裏面。 （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

你可以做到這一點，這樣既避免了這個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 
    ;