Suggest users based on common interest - MySql query - mysql

Question

Basically what i am trying to do is to suggest people based on common interests.
I have a table of Users(id, username, firstname, lastname, etc)
I have a table of Interested_People where UserID + Interested_in is stored.
I have a table of Contactlist where people who are added with each other is stored.(user1, user2, accepted [1,0])
What I want is to select * users table who are not my friend and they have same interest with me as well.
I searched a lot in internet but couldn't find something like so.
Here i do have created a query and it does exactly what I want. But it is very slow. Even it takes 16 to 20 second to output in PHPMyAdmin in my local machine. Now I Kindly request you guys if you can edit my query a bit and make it bandwidth & time efficient.
SELECT *
FROM users
WHERE id IN(SELECT userid
FROM interested_people
WHERE interested_in IN(SELECT interested_in
FROM interested_people
WHERE userid = [userid])
AND id NOT IN(SELECT user1 AS my_friends_userid
FROM contactlist f
WHERE f.user2 = [userid]
AND accepted = 1
UNION
SELECT user2 AS my_friends_userid
FROM contactlist f
WHERE f.user1 = [userid]
AND accepted = 1))
AND id != [userid]
ORDER BY Rand ()
LIMIT 0, 10;
[Userid] in this query is the ID of the user who is online. Like if i m online my ID will be 1.
This query suggest 10 random users who are not my friends and have same interests as me. But very slooow.
Thanks in advance!

Answer 1

Your problem suggests a self-join to get the users with common interests. Then, not exists to avoid the contact list. The following gets the list of users with common interests, ordered by the number of common interests:
select ip2.userid, count(*) as numInCommon
from interested_People ipme join
interested_People ip2
on ipme.interested_in = ip2.interested_in and
ipme.userid = $UserId and -- Your user id goes here
ip2.userid <> ipme.userid
where not exists (select 1
from contactlist cl
where cl.user1 = ipme.userid and cl.user2 = ip2.userid and
cl.accepted = 1
) and
not exists (select 1
from contactlist cl
where cl.user1 = ip2.userid and cl.user2 = ipme.userid and
cl.accepted = 1
)
group by ip2.userid;