SELECT *
  FROM `projects` AS A
 WHERE '○' = ALL(
     SELECT CASE WHEN `step_nbr` <= 1 AND status = "完了" THEN '○'
                 WHEN `step_nbr` >  1 AND status = "待機" THEN '○'
                 ELSE '×'
            END
       FROM `projects` AS B
      WHERE A.project_id = B.project_id
 )