query

SELECT *,
    (SELECT CLASS 
     FROM TABLE AS t2 
     WHERE t2.C = t1.C
       AND t2.R = t1.R
       AND t2.STEP_ID = 8) AS STEP_2_CLASS
FROM TABLE AS t1
WHERE (STEP_ID = 8 AND NOT EXISTS (
         SELECT *
         FROM TABLE t2
         WHERE t2.C= t1.C
            AND t2.R = t1.R
            AND t2.REVIEW_STEP_ID = 7
      ))
   OR (STEP_ID = 7)