MySQL的编码问题

Question

我怎样才能加入users与users_friends.user_id时user_id = '" . $user_id . "'

而且随着users_friends.friend_id加入users时friend_id = '" . $user_id . "'

如果user_id = '" . $user_id . "'

INNER JOIN users ON users_friends.user_id = users.user_id 

如果friend_id = '" . $user_id . "'

INNER JOIN users ON users_friends.friend_id = users.user_id 

当前的MySQL代码。

SELECT COUNT(user_id) as friends 
FROM users_friends 
WHERE (user_id = '" . $user_id . "' 
OR friend_id = '" . $user_id . "') 
AND friendship_status = '1' 

Answer 1

(SELECT * FROM users_friends JOIN users ON users.user_id = users_friends.friend_id 
    WHERE users_friends.friend_id = '" . $user_id . "') 
UNION 
(SELECT * FROM users_friends JOIN users ON users.user_id = users_friends.user_id 
    WHERE users_friends.user_id = '" . $user_id . "') 

像这样的事情可以做的工作。

当您在user_friends表中查找时，应该使用它与用户表联接。

Answer 2

如果我的理解是否正确，然后尝试这样：

call list_user_friends(1); 

call list_all_friends_of_user(1); 

完整的脚本：

-- TABLES 

drop table if exists users; 
create table users 
(
user_id int unsigned not null auto_increment primary key, 
username varbinary(32) unique not null 
) 
engine=innodb; 

drop table if exists user_friends; 
create table user_friends 
(
user_id int unsigned not null, 
friend_user_id int unsigned not null, 
primary key (user_id, friend_user_id) -- note clustered composite PK (innodb only) 
) 
engine=innodb; 

-- STORED PROCEDURES 

drop procedure if exists insert_user_friend; 

delimiter # 
create procedure insert_user_friend 
(
in p_user_id int unsigned, 
in p_friend_user_id int unsigned 
) 
proc_main:begin 

    if p_user_id = p_friend_user_id then 
    leave proc_main; 
    end if; 

    insert into user_friends (user_id, friend_user_id) values (p_user_id, p_friend_user_id); 

end proc_main # 

delimiter ; 

drop procedure if exists list_user_friends; 

delimiter # 
create procedure list_user_friends 
(
in p_user_id int unsigned 
) 
proc_main:begin 

    select 
    u.* 
    from 
    user_friends uf 
    inner join users u on uf.friend_user_id = u.user_id 
    where 
    uf.user_id = p_user_id 
    order by 
    u.username; 

end proc_main # 

delimiter ; 

drop procedure if exists list_all_friends_of_user; 

delimiter # 
create procedure list_all_friends_of_user 
(
in p_user_id int unsigned 
) 
proc_main:begin 

    select 
    u.* 
    from 
    users u 
    inner join 
    (
    select friend_user_id as user_id from user_friends where user_id = p_user_id 
    union 
    select user_id from user_friends where friend_user_id = p_user_id 
) all_friends 
    on u.user_id = all_friends.user_id 
    order by 
    u.username; 

end proc_main # 

delimiter ; 

-- TEST DATA 

insert into users (username) values ('f00'),('bar'),('alpha'),('delta'),('omega'),('theta'); 

call insert_user_friend(1,2); 
call insert_user_friend(1,3); 
call insert_user_friend(1,4); 
call insert_user_friend(1,1); -- oops 

call insert_user_friend(2,1); 
call insert_user_friend(2,5); 

call insert_user_friend(4,1); 

call insert_user_friend(6,1); 

-- TESTING (call these sproc from your php !) 

call list_user_friends(1); 

call list_all_friends_of_user(1);