sql - Merge overlapping time intervals, how?

Question

Anyone could help me in a query that **merge a interval of datas?
ex: Common select:

SELECT id, date_start, date_end FROM evento ORDER BY date_start

I GOT THIS:


FROM THIS:


but a want a query that return this:

01 - 2013-10-11 08:00:00 2013-10-11 15:00:00
02 - 2013-10-11 16:00:00 2013-10-11 19:00:00

Thanks a lot!

Answer 1

You may also try this query (once more solutions beside those given by PM 77-1 in the comment above) :

WITH RECURSIVE cte( id, date_start, date_end ) AS
(
  SELECT id, date_start, date_end
  FROM evento
  UNION 
  SELECT e.id,
         least( c.date_start, e.date_start ),
         greatest( c.date_end, e.date_end )
  FROM cte c
  JOIN evento e
  ON e.date_start between c.date_start and c.date_end
     OR 
     e.date_end between c.date_start and c.date_end
)
SELECT distinct date_start, date_end
FROM (
  SELECT id, 
         min( date_start) date_start, 
         max( date_end ) date_end
  FROM cte
  GROUP BY id
) xx
ORDER BY date_start;

Demo ---> http://www.sqlfiddle.com/#!12/bdf7e/9

however for huge table the performance of this query could be horribly slow, and some procedural approach might perform better.