MySQL JOIN语句cross join？

Question

我不擅长使用旧的JOIN语句，并且需要一些友好的帮助。我有两张表，假设是Employee表

   LastName DepartmentID
Rafferty    31
Jones   33
Steinberg   33
Robinson    34
Smith   34
John    NULL

和表Department

DepartmentID    DepartmentName
31  Sales
33  Engineering
34  Clerical
35  Marketing

如果我想返回where DepartmentID=31和only results where Employee.DepartmentID = Department.DepartmentID的结果，那么返回的结果将如下所示：

Employee.LastName   Employee.DepartmentID   Department.DepartmentName
Rafferty    31  Sales

(我们可以去掉其中一个DepartmentID，因为它们是相同的)-实现这一点的SQL语句是什么？

谢谢

Answer 1

SELECT e.LastName, e.DepartmentID, d.DepartmentName
FROM Employee e
INNER JOIN Department d ON d.DepartmentID = e.DepartmentID
WHERE d.DepartmentID = 31

Answer 2

这里有一个比喻鱼：

SELECT * FROM employee INNER JOIN部门on employee.departmentId = department.departmentId WHERE departmentId = 31

这是一个比喻式的钓鱼经验：

http://www.w3schools.com/sql/sql_join.asp (只需按“下一步”)

Answer 3

SELECT e.LastName, e.DeparmentID, d.DepartmentName
FROM employee AS e INNER JOIN department AS d ON e.DepartmentID = e.DepartmentID
WHERE e.DepartmentID = 31

我们将使用一个INNER JOIN来匹配每个表中的记录，方法是使用ON部分->来使两个表之间的departmentd值相等。