SQL - CASE example

SELECT A.data_queue_name, 
       A.data_queue_library,  
       A.current_messages, 
       B.current_messages, 
CASE 
    WHEN 
      A.current_messages = B.current_messages 
        THEN ' ' 
        ELSE '**diff**' 
END
FROM swtgemts1 A JOIN swtgemts2 B ON A.data_queue_name = B.data_queue_name;