Mysql Join for 3 tables - mysql

Question

I have checked former posts and none has solved my problem yet, any help would be appreciated
MYSQL query to 3 tables (Users, Match, Interview)
Want to return the users name and interview # (if there is an interview number) for the specified Match.
But I do not want to limit the results to only users who have an interview. I tried JOIN, but cannot get it to work for 3 tables.
Here is what I have so far in PHP:
$query = "SELECT CONCAT(u.first_name,' ',u.last_name,'----',COALESCE(i.v_code,'')) as name, u.id as id
FROM #__users as u
JOIN #__bl_match as m ON ( (u.team_id = m.team1_id) OR
(u.team_id = m.team2_id) OR
(u.team_id = m.team3_id AND m.team3_id != 0) OR
(u.team_id = m.team4_id AND m.team4_id != 0) OR
(u.team_id = m.team5_id AND m.team5_id != 0) OR
(u.team_id = m.team6_id AND m.team6_id != 0) OR
(u.team_id = m.team7_id AND m.team7_id != 0) OR
(u.team_id = m.team8_id AND m.team8_id != 0) OR
(u.team_id = m.team9_id AND m.team9_id != 0) OR
(u.team_id = m.team10_id AND m.team10_id != 0))
AND m.id = ".$t_id."AND m.id != 0
JOIN #__bl_interview as i ON i.u_id = u.id";
$db->setQuery($query);
$parti12 = $db->loadObjectList();

Answer 1

If you want Users with no Interview, you'll need to use a LEFT JOIN to the interview table, but that means the interview number for that user will be NULL.
Since you're concatenating the number with the user name in your SELECT list, this results in the user's name being returned as NULL when they've got no interviews (since concatenating a string with a NULL value - or performing pretty much any other operation on a NULL value - produces a NULL result).
To avoid this, you must handle the case when i.v_code is NULL. The typical way to do that in MySQL is with the COALESCE function:
SELECT CONCAT(u.first_name, ' ', u.last_name, '----', COALESCE(i.v_code,'')) as name,
u.id as id
FROM #__users as u
JOIN #__bl_match as m ON ( (u.team_id = m.team1_id) OR
(u.team_id = m.team2_id) OR
(u.team_id = m.team3_id AND m.team3_id != 0) OR
(u.team_id = m.team4_id AND m.team4_id != 0) OR
(u.team_id = m.team5_id AND m.team5_id != 0) OR
(u.team_id = m.team6_id AND m.team6_id != 0) OR
(u.team_id = m.team7_id AND m.team7_id != 0) OR
(u.team_id = m.team8_id AND m.team8_id != 0) OR
(u.team_id = m.team9_id AND m.team9_id != 0) OR
(u.team_id = m.team10_id AND m.team10_id != 0))
AND m.id = ".$t_id."AND m.id != 0
LEFT JOIN #__bl_interview as i ON i.u_id = u.id"
Now, given the formatting you're applying to the name, you may be left with an extraneous ---- after the name with no subsequent interview code. If you'd like to avoid that, we can use IF instead of COALESCE to get a little smarter with our output, like so:
SELECT CONCAT(u.first_name, ' ', u.last_name, IF(i.v_code, '---- ' + i.v_code, '')) as name
Note what that's doing: if i.v_code is not NULL, the first expression in the IF evaluates to true, so the second expression is returned. Otherwise, the third expression (the empty string) is returned - so when i.v_code is NULL, you only output the user's name.