text: SET sql_mode = '';
  SELECT Start_Date, End_Date
  FROM 
      (SELECT Start_Date FROM Projects WHERE Start_Date NOT IN (SELECT End_Date FROM Projects)) a,
      (SELECT End_Date FROM Projects WHERE End_Date NOT IN (SELECT Start_Date FROM Projects)) b 
  WHERE Start_Date < End_Date
  GROUP BY Start_Date 
  ORDER BY DATEDIFF(End_Date, Start_Date), Start_Date