SELECT 
    w.testID
  , s.subject
  , t.subjectID 
  , DATE_FORMAT(w.valid_from, "%d.%m.%Y, %H:%ih")   AS startTime
  , DATE_FORMAT(w.valid_until, "%d.%m.%Y, %H:%ih")  AS endTime
  , CASE 
       WHEN now() BETWEEN w.valid_from AND w.valid_until  THEN 1
                                                          ELSE 0
    END AS withinTimeFrame
FROM
  mc_test_schedule w
LEFT JOIN
  mc_test t
  ON t.ID = w.testID
LEFT JOIN
  mc_subject s
  ON s.ID = t.subjectID 
WHERE
   w.valid_until >= now()
   --->