I had an occasion to expand Don’s query a bit to produce a list of users, locations, & emails for all users with a location entered. Might be interesting or useful in some cases:
SELECT u.username, u.locale, up.location, ue.email
FROM users u
LEFT JOIN user_profiles up ON u.id = up.user_id
LEFT JOIN user_emails ue ON u.id = ue.user_id
-- comment out WHERE clause for complete user list
WHERE up.location <> ''
ORDER BY up.location