K tomu slouží LEFT JOINy:
SELECT bug_id, `desc`, dev.assigned_to, qa.qa_contact
FROM bugs
INNER JOIN profiles as dev ON bugs.assigned_to = dev.userid
LEFT OUTER JOIN profiles as qa ON bugs.qa_contact = qa.userid
K tomu slouží LEFT JOINy:
SELECT bug_id, `desc`, dev.assigned_to, qa.qa_contact
FROM bugs
INNER JOIN profiles as dev ON bugs.assigned_to = dev.userid
LEFT OUTER JOIN profiles as qa ON bugs.qa_contact = qa.userid