MYSQL left join on multiple fields

Question

I have a friends table. Is it possible to do a left join on two fields of the table. In other words, I don't know which of the two fields may have the match I need. If not is there another way to do this?

$sql = "SELECT * FROM `friends` f
LEFT JOIN `users` u
ON f.askee OR f.asker = u.ID
where (asker='$userid' OR askee='$userid') AND status='3'";

Answer 1

The left join is correct: the OR operator will do what you expect. But then your filter on $userid should apply to the parent table (friends), not left joined one (otherwise it would cancel the outer join):

$sql = "SELECT * FROM `friends` f
LEFT JOIN `users` u ON f.`askee` = u.`ID` OR f.`asker` = u.`ID`
WHERE u.`status` = '3' AND u.ID = '$userid'";