Example query:

SELECT DISTINCT u.id, u.username, u.realname, u.access_level as access_level, l.access_level as override
FROM mantis_user_table u
LEFT JOIN ( mantis_project_table p LEFT JOIN mantis_project_user_list_table l ON p.id=l.project_id AND p.id = 1 ) ON l.user_id=u.id
WHERE ( ( u.access_level >= 55 ) OR ( l.access_level >= 55 AND l.user_id=u.id ) OR u.access_level>=90 ) AND u.enabled = 1 AND p.id = 1