SELECT    DISTINCT messagetype.*
FROM      messagetype
LEFT OUTER JOIN BUSINESSCHANNEL bc ON
    bc.idMessageType = messagetype.idMessageType
    AND bc.direction = 'out'
LEFT JOIN partnersystemmessages ON
    messagetype.idMessageType = partnersystemmessages.idMessageType
      AND partnersystemmessages.idSystem = 522
WHERE     partnersystemmessages.idMessageType IS NULL