使用php和mysql从所有用户的朋友中检索用户配置文件数据

Question

I searched several examples on the web and still need some help after researching. I have 2 tables: users and friends.

the users table has columns:

• id bigint(20)UNSIGNED AUTO_INCREMENT
• username varchar(50)
• profile_picture varchar(200)
• status varchar(20)
• status_message varchar(200)

the friends table has columns:

• id bigint(20) UNSIGNED AUTO_INCREMENT
• initiator_user_id bigint(20)
• friend_user_id bigint(20)

I want to be able to get the username, profile_picture, status, status_message from all users who are friends (friend_user_id) of a specified user (initiator_user_id). After researching I believed this is done with a union.

I have tried the query below but it doesn't work:

SELECT friend_user_id 
FROM friends
WHERE initiator_user_id = 1001 //gets all the id's of the friends of user 1001
UNION All
SELECT profile_picture, status, status_message, username from users
WHERE friend_user_id = id //gets all the profile data of user's profiles that are friends of user 1001

What I need is for the friends data to be displayed for all friends:

• id bigint(20)UNSIGNED AUTO_INCREMENT
• username varchar(50)
• profile_picture varchar(200)
• status varchar(20)
• status_message varchar(200)

My questions:

• Does anything need to be changed regarding the tables (any foreign key constraints...etc.)?
• What do I need to change to make this example work?

Answer 1

Use a simple INNER JOIN:

SELECT u.*
FROM users AS u
INNER JOIN friends AS f ON f.friend_user_id = u.id
WHERE f.initiator_user_id = 1001