Mysql, search in multiple tables - mysql

Question

I'm working on an async game, but I'm totally new to MySQL and PHP. I have two tables, tb_users and tb_matches. The first one stores all users and their status (for example, a value of 0 in the 'status' column means the player is in stand-by, while a value of 1 means the player is waiting for an opponent to play a match).
The tb_matches table stores all the matches, both active and inactive (completed) ones. There are two columns in this table with player IDs.
What I am trying to do is to perform a search for an available opponent, which must fulfill these requirements:
1) it must have a status of 1 in the tb_users table
2) it must not already have an active match with the user searching for a new opponent
I've tried with:
SELECT *
FROM tb_users
JOIN tb_matches
WHERE tb_users.status = "1"
AND tb_matches.player1 != '".$username."'
AND tb_matches.player2 != '".$username."'
..but it's not giving me any result. Also, it should take into account that in the tb_matches table, there could be no matches at all.
Any help? Also, is there a better way to accomplish this task?

Answer 1

Consider the following alternate table structure:
tb_users
---------
id
name
seeking
tb_user_matches
---------------
match_id
player_id
tb_matches
----------
id
started
ended
status
Adding a third (many-to-many) table to store which players are involved in which match allows simpler queries, see below.
Change "status" in tb_users to "seeking" so a boolean data type makes sense.
Don't store player names in tb_matches, store their ID. (Allows name changes without breaking links (Normalization).)
Consider adding datetime fields to tb_matches to store the match start and end date; it might be useful in the future.
The "status" column in tb_matches can indicate three match statuses: waiting for more players, in progress, or completed (see below).
With this structure, you can use the following query to find players that are:
Searching for a match (seeking = 1)
Not already in a match that is waiting for players
SELECT u.id, u.name
FROM tb_users u
LEFT JOIN tb_user_matches um
JOIN tb_matches m
ON um.match_id = m.id AND m.status = 0
ON u.id = um.player_id
WHERE u.seeking = 1
AND um.match_id IS NULL;
I am proposing tb_matches.status could be "0" for inactive (waiting for players), "1" for active, and "2" for completed.
This does not necessarily check if the player is already engaged in an active match. Perhaps your game allows players to participate in multiple simultaneous matches? If not, you can alter the query to exclude matches that are active as well (change m.status = 0 to m.status != 2).
Edit:
To explain the query in English (as best I can):
Select user id and name from the users table. Include matches that the user is involved where the match status is "0" (waiting). (The LEFT JOIN makes it so if the user is not involved in any matches with status "0", the match_id will be empty (null).)
Now, from this set of data, only show users that are seeking (u.seeking = 1), and aren't in a waiting match (um.match_id IS NULL).

Answer 2

Try this (note that you will have to substitute 'username' for the actual user name)
SELECT *
FROM tb_users
WHERE Username != 'username'
AND status = 1
AND NOT EXISTS (SELECT *
FROM tb_matches
WHERE (player1 = 'username' OR player2 = 'username')
AND Status = 'inactive')

Answer 3

SELECT *
FROM
`tb_users`
WHERE
`tb_users`.`status` = "1"
AND
`tb_users`.`name` NOT IN (
SELECT `player1` FROM `tb_matches` WHERE `player2` = 'username'
UNION
SELECT `player2` FROM `tb_matches` WHERE `player1` = 'username'
UNION
SELECT 'username'
)