如何從兩個表計數，而子查詢在MySQL

Question

我有兩個表，

department 
———- 
deptid (type: INT) 
deptname (type: TEXT) 
hours (type: INT) 
active (type: BIT) 

employee 
——– 
empid (type: INT) 
empname (type: TEXT) 
deptid (type: INT) 
designation (type: TEXT) 
salary (type: INT) 

現在該怎麼做查詢，而無需使用子查詢返回的列empname和屬於那些有部門員工的deptname人數在4人以上。記錄應按字母順序重新輸入。

Answer 1

因爲你有一個合一條件（4個或更多的頭數），這意味着沒有子查詢，你不能得到empname但只有deptname。

Answer 2

Select E.empName, D.DeptName, count(E2.EmpID) 
FROM Department D 
LEFT JOIN Employee E 
    ON E.DeptID = D.DeptID 
LEFT JOIN Employee E2 
    ON E.DeptID = D.DeptID 
GROUP BY E.EmpName, D.DeptName 
Having count(e2.empID) >=4 

Answer 3

我沒有測試過，但是這看起來我的權利

SELECT empname, deptname, department.deptid 
FROM employee JOIN department ON employee.deptid = department.deptid 
GROUP BY department.deptid 
HAVING count(department.deptid) >= 4 
ORDER BY empname;