PHP和MySQL上的Friendsystem

Question

at this moment I'm stucked on my code.

I want to display the names of accepted friends.

I have two tables:

Users 
[id, useruniqueid, username]

Friends
[id, user_a, user_b, status]

(status can be requested, pending or accepted)

For example:

Users:
1, 123, Kaan2106
2, 321, SOUser1
3, 456, SOU2
4, 654, Some4

Friends:
1, 123, 321, accepted
2, 321, 123, accepted
3, 456, 123, accepted
4, 123, 456, accepted
5, 654, 123, pending
6, 123, 654, requested

I want to display my friend(s) names like: "SOUser1" (because it's accepted)

And this is what I done:

<table>
<tr>
    <td>Name</td>
</tr>
<?php
$getem = mysql_query("SELECT * FROM Friends WHERE (`status` = 'accepted') AND (`user_a` = '$UserUUID' OR `user_b` = '$UserUUID') LIMIT 10");
while($row = mysql_fetch_assoc($getem)) {
    $friendsql = mysql_query("SELECT * FROM Users WHERE useruniqueid = '" . ($row['user_a'] == $UserUUID ? $row['user_b'] : $row['user_a']) . "'");
    $friendrow = mysql_fetch_assoc($friendsql);
?>
<tr>
    <td class="friend-name">
        <?php echo $friendrow['username']; ?>
    </td>
</tr>
<?php } ?>
</table>

And my output is like this SOUser1, SOUser1, SOU2, SOU2 (unwanted doubles)

The expected output should be like this SOUser1, SOU2 (no doubles)

I know that mysql_* is deprecated

Answer 1

If you do it all in one query (with a join), you can use MySQL's distinct operator to only return one instance of each user's name.

Try using a query like the one below. The join uses a case statement so that it joins the Friends table by either user_a or user_b, depending on which one is not the $UserUUID.

select distinct
    u.username
from
    Friends f
    join Users u
        on (
            u.useruniqueid = case
                                when f.user_a='{$UserUUID}' then f.user_b
                                else f.user_a
                            end
            )
where
    (f.user_a = '{$UserUUID}' or f.user_b = '{$UserUUID}')
    and f.status='accepted'

See it in an SQL Fiddle, with $UserUUID being set to '123'.