MySQL search different tables and only fetch specfic IDs

MySQL search different tables and only fetch specfic IDs

I am trying to create an algorithm to sort out the most relevant data for
a specific user_id.
I imagine my end result to be an array with KEY as the found USER_ID and
the VALUE to be the number of times the specific USER_ID has been found in
the different rows.
So, I need to look through different rows in different tables and look for
where CURRENT_USER_ID (lets say id: 30) exists, and then find the
RECIEVER_ID, that is the user which was communicated to. This is pretty
hard to explain, but lets take an example:
I have a table called: edu_posts, which contains wallposts and comments to
theese. The are different values in this table, but the ones we should
focus on is: post_author and post_reciever. We then have to look for all
the rows where post_author equals 30 (the test example; just needs to be
the current users id) and then print out the post_reciever IDS. This would
be easy enough with a single query, but lets say we have to find data in 5
or 10 different tables, that 10 different queries, which is a lot.
We also have a table called edu_folowers. There we have to look for where
follow_author equals 30 (the test example; just needs to be the current
users id), and then print out the follow_user ID. Again, to find out who
the current user have interest in.
I image the final mysql_fetch to look something like this:
user_id => 25
times_found => 5
user_id => 11
times_found => 3
user_id => 95
times_found => 1
etc.
Can this be done using a single query, maybe using JOIN? And even maybe
count the results IN the query, so I don't have to do this manually in the
PHP code.
Or should I create a mysql_query for every table I wish to get data from,
and then manage the data afterwards using PHP? This sounds like the
easiest way to me, but also the most inefficient relating to script
optimization.
I have tried out with the following test-query:
SELECT
u.user_id AS user_id,
f.follow_user AS user_id_follow,
p.post_reciever AS user_id_posts
FROM
`edu_posts` u
LEFT JOIN `edu_followers` f ON f.follow_author = '30'
LEFT JOIN `edu_posts` p ON p.post_author = '30' && p.post_reciever != '30'
WHERE
u.user_id = '30'
GROUP BY
f.follow_id, p.post_id
But the problem is that it outputs unexcepted results, and also I will
have different values to look for, fx: user_id (not really needed, as we
already know that it is 30), user_id_follow, user_id_posts, and so on.
I hope you understand my question, and please let me know, if you need
additional information.
Many thanks in advance!