sql 新手求助

Question

新手才学sql 不久  对个习题不解
表结构如下要求Show 员工所在的the department id 名字 和 employees 的个数（其所在的department的人数少于4个）感谢！

Answer 1

如果还想关联出部门名称，你得关联部门表，而你并没有提供部门表
SELECT DEPARTMENT_ID,COUNT(EMPLOYEE_ID)FROM TB HAVING COUNT(EMPLOYEE_ID)<4

Answer 2

SELECT  a.*,b.Department_Name,c.DepartmentEmployeeCount
FROM    Employee AS a
        INNER JOIN Dept AS b ON a.Department_ID = b.Department_ID
        INNER JOIN (SELECT Department_ID,COUNT(1) AS DepartmentEmployeeCount FROM Employee GROUP BY Department_ID ) AS c ON c.Department_ID=a.Department_ID
        
        
        

Answer 3

SELECT DEPARTMENT_ID,COUNT(EMPLOYEE_ID) AS 个数
FROM TB 
GROUP BY DEPARTMENT_ID
HAVING COUNT(EMPLOYEE_ID)<4

Answer 4

忘加GROUP BY了SELECT DEPARTMENT_ID,COUNT(EMPLOYEE_ID)FROM TB GROUP BY DEPARTMENT_ID HAVING COUNT(EMPLOYEE_ID)<4