我需要加入一个表和一个子查询

Question

SELECT * FROM Employee
(
   SELECT eid  FROM Assignment
   GROUP BY eid
   HAVING SUM(hours_per_week) > 40
)

这是我的代码，用于查找超过40的hours_per_week。子查询返回超过40小时的人的eid。 我的问题是如何使用从子查询中获得的eid显示Employee中的所有人员。 在哪里？ 还是加入？

Answer 1

使用WHERE ... IN (SELECT ...)

SELECT col1, col2, ..., coln
FROM Employee
WHERE eid IN
(
   SELECT eid  FROM Assignment
   GROUP BY eid
   HAVING SUM(hours_per_week) > 40
)

Answer 2

SELECT e.*
FROM Employee AS e
INNER JOIN
(
   SELECT eid
   FROM Assignment
   GROUP BY eid
   HAVING SUM(hours_per_week) > 40
) AS ot ON ot.eid = e.eid

Answer 3

Select E.EID, sum(A.hours_per_Week)
FROM employee E 
INNER join Assignment A on E.EID = A.EID
Group By E.EID 
Having sum(A.Hours_per_week) > 40

你为什么需要子查询？