Untitled

SELECT START_DATE, X FROM (
    SELECT A.START_DATE, MIN(B.END_DATE) AS X
    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 A.START_DATE
) P
ORDER BY DATEDIFF(X, START_DATE), START_DATE;