Untitled

SELECT start_date, MIN(end_date)
FROM 
    (SELECT start_date FROM projects WHERE start_date NOT IN (SELECT end_date FROM projects)) taskstart,
    (SELECT end_date FROM projects WHERE end_date NOT IN (SELECT start_date FROM projects)) taskend
where start_date < end_date
GROUP BY start_date
ORDER BY datediff(start_date, MIN(end_date)) DESC, start_date