有沒有可能通過計數（不同）沒有加入一個組？

Question

Table 1 : (Company) 

ID Name 
1 A 
2 B 
3 C 

每個公司（pk = ID）都可以有一個或多個員工。

Table 2 : (Employee) (CompanyID referencing ID) 

CompanyID EmpID Name 
1   1  Joe 
1   2  Doe 
1   3  Boe 
2   4  Lou 
3   5  Su 
3   6  Ram 

查詢：

select CompanyID, count(*) from Employee group by CompanyID having count(*) > 1; # Lists companies and their counts. 

CompanyID count(*) 
1   3 
3   2 

對於此查詢，我只想要一個結果，具有鮮明的CompanyIDs的計數。因此，在這種情況下，'2'[公司A和C]。

總之，我正在尋找擁有2名或更多員工的公司數量。

反正有沒有臨時表或連接得到結果？我正在使用MySQL。

Answer 1

是：

select count(*) from 
(select CompanyID from Employee group by CompanyID having count(*) > 1) v 

或範圍：

select count(*) from 
(select CompanyID from Employee group by CompanyID 
having count(*) >= 5 and count(*) < 10) v 

Answer 2

是的，這可能與子查詢：

SELECT COUNT(*) 
FROM 
    (SELECT 1 
    FROM Employee 
    GROUP BY CompanyID 
    HAVING COUNT(*) > 1 
) AS grp 

或：

SELECT COUNT(DISTINCT CompanyID) 
FROM Employee AS e 
WHERE EXISTS 
     (SELECT * 
     FROM Employee AS e2 
     WHERE e2.CompanyID = e.CompanyId 
      AND e2.EmpID <> e.EmpID 
    ) 

或許如果COUNT(*)很慢，你可以使用MIN()和MAX()：

SELECT COUNT(*) 
FROM 
    (SELECT 1 
    FROM Employee 
    GROUP BY CompanyID 
    HAVING MAX(EmpID) > MIN(EmpId) 
) AS grp