HackerRank MySQL - SQL Project Planning

You are given a table, Projects, containing three columns: Task_ID, Start_Date and End_Date. It is guaranteed that the difference between the End_Date and the Start_Date is equal to 1 day for each row in the table.

SELECT START_DATE, MIN(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 (MIN(END_DATE) - START_DATE), START_DATE;