I have two mysql queries that return a column of phone numbers. I want am trying to end up with a list of phone numbers that are in one list, but not in the other. So the two queries I have are: SELECT phone FROM civicrm_phone phone LEFT JOIN civicrm_participant participant ON phone.contact_id = participant.contact_id WHERE phone.is_primary = 1 AND participant.id IS NULL and SELECT phone FROM civicrm_phone phone LEFT JOIN civicrm_participant participant ON phone.contact_id = participant.contact_id WHERE phone.is_primary = 1 AND participant.id IS NOT NULL And before anyone asks, the above two queries do not provide mutually exclusive results (based on using IS NULL and IS NOT NULL for the last WHERE statement), since we have related individuals in the database who use the same phone number, but do not necessarily all have a participant.id. Thanks for any help.