如何編寫一個MySQL Join查詢

Question

我有兩個表。

users: 
     uid | city  | username | flag | 
     10 | New York | john  | 1 | 
     14 | Tokyo | kawasaki | 1 | 
     15 | Tokyo | coder | 1 | 

groupmember: 
     id | uid | groupid | 
     1 | 10 | 16  | 
     2 | 14 | 16  | 
     3 | 15 | 21  | 

這兩個表中的'uid'都是一樣的。

我想選擇所有在城市「東京」的用戶，這些用戶也在groupid爲「16」的組中。

所以查詢resutl應該是（在這種情況下）

14 | Tokyo | kawasaki | 1 | 

Answer 1

SELECT u.uid, u.city, u.username, u.flag 
FROM users u 
JOIN groupmember g ON u.uid = g.uid 
WHERE u.city = 'Tokyo' 
    AND g.groupid = 16; 

Answer 2

select u.* from users u join groupmember gm on u.uid = gm.uid 
where u.city='Tokyo' and gm.groupid=16 

Answer 3

SELECT u.uid, u.city, u.username, u.flag 
FROM users u, groupmember g 
WHERE u.uid = g.uid 
    AND u.city = 'Tokyo' 
    AND g.groupid = 16; 

Answer 4

SELECT * FROM 
    users INNER JOIN groupmember 
     ON users.uid = groupmember.uid 
     AND groupmember.groupid = 16 
     AND users.city = 'Tokyo'