mysql - 嵌套查询的问题

Question

嘿伙计们，我一直在研究这个问题，但我无法解决它。有人可以帮我解决这个问题吗？我尝试了很多方法但无法解决它，任何人都可以通过使用嵌套查询并仅使用(GROUP BY、HAVING、SELECT、FROM 和 WHERE)来帮助我

(Qs)You would like to know the departments with more than 5 full-time young employees (Age <25) each department has. Calculate the average salary of the employees who work for those departments. This newly calculated field should be named as "AvgSalary" and be returned by your query.

这是其架构。

Employee(EmployeeID: Integer, EmpName: String, Age: Integer, Salary: Real)  
Department(DeptID: Integer, DeptName: String, Budget: Real, ManagerID: Integer)
Works(EmployeeID: Integer, DeptID: Integer, Percent_Time: Integer)

Answer 1

如果您只对目标群体(25 岁以下)的平均工资感兴趣，则不需要嵌套...

SELECT d.*
     , AVG(********) AvgSalary 
  FROM ******** 
  JOIN ********
    ON ******** = ******** 
  JOIN ********  
    ON ******** = ******** 
 WHERE ******** = 100 
   AND ******** < 25 
 GROUP 
    BY ******** 
HAVING COUNT(*) > 5; 

如果您需要目标组返回的部门内所有员工的平均工资，那么您可以使用子查询，但我会使用 CASE 语句，