MySQL matches row tables with overlapping date ranges

Question

I have a temporary table with overlapping dates available. These dates can be overridden by any combination of methods, as they are intended for several available rooms.

I would like to create a query that returns a consolidated set of available dates. (Opening date is available day, closing is not available.)

For example, the following data

+------------+------------+
|   opens    |   closes   |
+------------+------------+
| 2015-12-03 | 2015-12-05 |
| 2016-01-08 | 2016-01-15 |
| 2016-02-21 | 2016-02-27 |
| 2016-03-13 | 2016-03-24 |
| 2016-03-31 | 2016-04-02 |
| 2016-04-06 | 2016-04-15 |
| 2016-04-21 | 2016-12-03 |
| 2015-12-03 | 2015-12-09 |
| 2016-01-03 | 2016-01-06 |
| 2016-01-16 | 2016-02-08 |
| 2016-03-01 | 2016-03-06 |
| 2016-03-10 | 2016-12-03 |
+------------+------------+

Must return:

+------------+------------+
|   opens    |   closes   |
+------------+------------+
| 2015-12-03 | 2015-12-09 |
| 2016-01-03 | 2016-01-06 |
| 2016-01-08 | 2016-01-15 |
| 2016-01-16 | 2016-02-08 |
| 2016-02-21 | 2016-02-27 |
| 2016-03-01 | 2016-03-06 |
| 2016-03-10 | 2016-12-03 |
+------------+------------+

Thank you for your help!

Answer 1

One way to do this is to use correlated subqueries:

SELECT DISTINCT
       (SELECT MIN(opens)
       FROM mytable AS t2
       WHERE t2.opens <= t1.closes AND t2.closes >= t1.opens) AS start,
       (SELECT MAX(closes)
       FROM mytable AS t2
       WHERE t2.opens <= t1.closes AND t2.closes >= t1.opens) AS end       
FROM mytable AS t1
ORDER BY opens

Predicates WHEREfor correlated subqueries:

t2.opens <= t1.closes AND t2.closes >= t1.opens

, . , : - opens , - closes.

EDIT:

, :

1. |-----------|
2. |----|
3.           |-----|

. 2, , .

:

SELECT MIN(start) AS start, MAX(end) AS end
FROM (
  SELECT @grp := IF(@start = '1900-01-01' OR 
                   (opens <= @end AND closes >= @start), @grp, @grp+1) AS grp,        
         @start := IF(@start = '1900-01-01', opens, 
                      IF(opens <= @end AND closes >= @start, 
                         IF (@start < opens, @start, opens), opens)) AS start,
         @end := IF(@end = '1900-01-01', closes, 
                    IF (opens <= @end AND closes >= @start, 
                      IF (@end > closes, @end, closes), closes)) AS end                 
  FROM mytable
  CROSS JOIN (SELECT @grp := 1, @start := '1900-01-01', @end := '1900-01-01') AS vars
  ORDER BY opens, DATEDIFF(closes, opens) DESC) AS t
GROUP BY grp

, opens/closes . @start, @end ( ) . , [@start - @end] , , grp .