MySQL查詢發現與員工的最低平均年齡

Question

我給出這個模式的部門：

Emp(eid: integer,ename: string,age: integer,salary: real) 
Works(eid:integer,did: integer,pct_time: integer) 
Dept(did:integer,budget: real,managerid:integer) 

我寫此查詢列出了部門代碼與員工蠻好的平均年齡一起：

SELECT d.did AS Department, AVG(e.age) AS Average_Age 
FROM Emp e, Works w, Dept d 
WHERE e.eid=w.eid AND w.did=d.did 
GROUP BY d.did 

然而，當我嘗試做這樣的事情：

SELECT Department, MIN(Average_Age) 
FROM 
(
SELECT d.did AS Department, AVG(e.age) AS Average_Age 
WHERE e.eid=w.eid AND w.did=d.did 
GROUP BY d.did 
) MyTable 

它返回WRO部門編號。它僅爲該列返回0，但它返回上一個表的最小年齡。但是，年齡最小的部門ID是4.我做錯了什麼？

Answer 1

請你試試這個：

SELECT department, MIN(avg_age) 
FROM 
(
    SELECT dept.did AS department, AVG(emp.age) AS avg_age FROM dept 
    LEFT JOIN works ON works.did = dept.did 
    LEFT JOIN emp ON emp.eid = works.eid 
    GROUP BY dept.did 
) AS test 
ORDER BY 1 LIMIT 1;