mysql - MySQL 帮助 - 哪些员工在一项任务上工作超过 50 小时？使用子查询？

Question

我有 2 张桌子，分配和员工。它们通过 EmployeeNumber 链接，而 HoursWorked 是存储在 assignment 中的一个属性。我已经尝试过了，我得到一个错误，说子查询返回超过 1 行。我究竟做错了什么：

SELECT e.FirstName, e.LastName
FROM employee e
WHERE (
    SELECT a.HoursWorked
    FROM assignment a
    WHERE a.HoursWorked > 50); 

Answer 1

看起来你正在尝试做这样的事情：

SELECT e.FirstName, e.LastName
FROM employee
JOIN assignment on employee.EmployeeNumber = assignment.EmployeeNumber
WHERE assignment.HoursWorked > 50;

Answer 2

SELECT e.FirstName, e.LastName FROM employee e WHERE e.EmployeeNumber IN ( SELECT EmployeeNumber FROM assignment a WHERE a.HoursWorked > 50);