Sometimes we'd like to list users who have registered with a Drupal site, but haven't been placed into any proper roles yet via subscriptions, purchases, membership approval or whatever.

Try this join query to get started:

SELECT users.uid, name, created, access, login, status
FROM {users}
LEFT OUTER JOIN {users_roles}
ON users.uid = users_roles.uid
WHERE users_roles.uid IS NULL AND users.uid != 0