mysql:
WITH raw1 as(SELECT 
															Task_ID, 
															Start_Date, 
															End_Date, 
															LAG(End_Date) OVER(ORDER BY End_Date) as E1 
												FROM projects), 
raw2 AS(SELECT 
											Task_ID, 
											Start_Date, 
											End_Date, 
											(CASE WHEN E1=Start_Date AND End_Date-E1=1 THEN 1 ELSE 0 END) AS binary1 
									FROM raw1 
									GROUP BY 1,2,3), 
raw3 AS(SELECT 
													task_ID, 
													Start_Date, 
													End_Date, 
													SUM(CASE WHEN binary1 = 0 THEN 1 ELSE 0 END) OVER (ORDER BY Task_ID ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)) AS project_label FROM raw2) SELECT MIN(Start_Date),MAX(End_Date) FROM raw3 GROUP BY project_label ORDER BY COUNT(project_label) ASC, Start_Date ASC