Multiple WHERE clause query doesn't work - sql

Question

EDIT: I've edited this question.
Here, $id = $_SESSION['id'] and let's say $id = 1 (Paul).
EVENTS
sender recipient type
1 2 message
2 4 like
USERS
id firstname
1 paul
2 anna
CONNECTION
subscribing subscribed
1 2
Here's where I am at right now:
SELECT events.sender, events.recipient, events.type, users.firstname, users.lastname,
connection.subscribing, connection.subscribed
FROM events, users, connection
WHERE events.sender=users.id
AND connection.subscribing =$id`
The goal of this query is to JOIN events and info from user 2 (Anna) since user 1 (Paul) has subscribed to her feed (in the connection list). User 1 should only see events + info from users he has subscribed to (here, Anna only)
My current query doesn't work for the following reasons:
1) Rows are duplicate
2) No matter the value of $id, all the rows from the table events show up: the filter
doesn't work.
Any ideas how to fix it?

Answer 1

I'm not sure about what is your goal, but here is some samples:
SELECT u.id, u.firstname, sender, recipient, post_id, type
FROM events e
inner join users u
ON (e.sender = $id) -- why you need additional table there?
inner join post_list p
ON (e.post_id = p.post_id)
Another example:
SELECT u.id, u.firstname, sender, recipient, post_id, type
FROM events e, users u, connection c, post_list p
where
e.sender=u.id AND
e.post_id=p.post_id AND
u.id=c.subscribed AND
u.id=$id
Last quest will return Cartesian product of all tables and "filter" only proper ones, you can safely replace query above with JOIN syntax (be careful with tables order):
SELECT u.id, u.firstname, sender, recipient, post_id, type
FROM events e
inner join post_list p
ON (e.post_id = p.post_id)
inner join users u
ON (e.sender = u.id AND u.id=$id)
inner join connection c
on (u.id = c.subscribed)
---- UPDATE
here is proper query:
select u.id, u.firstname, e.sender, e.recipient, e.type
from users u inner join events e on (u.id=.e.sender) -- this query return ALL events
-- next part "filters" results
where
u.id in (select subscribed from connection where subscribing=$id)
also you can move filter condition in ON clause
select u.id, u.firstname, e.sender, e.recipient, e.type
from users u inner join events e on (u.id=.e.sender and u.id in (
select subscribed from connection where subscribing=$id))
for performance reasons, I suggest to use another variant:
select e.* from events e
where e.sender in (select c.subscribing from connection c where c.subscribed=$id)
this query return all events, without user's information. All users should be stored in memcache (for example) and during output to page you can add user's names, avatars, etc
also, you can loop over results via php and get list of users which should be displayed, and fetch information from db only for them, sometimes this will be faster, try benchmarking all variants

Answer 2

If I'm understanding your question and table schemas correctly, this should work for you:
select u.id, u.firstname,
e.sender, e.recipient, e.post_id, e.type,
pl.post
from events e
join users u on e.sender != u.id
join connection c on c.subscribed = e.sender
join post_list pl on e.post_id = pl.post_id
where e.sender = $id
I don't exactly understand your relationship between events and users, but this should get you going in the right direction.
A Visual Explanation of SQL Joins