Question

I have a table of available date blocks (7 days in my case) which may or may not be consecutive:

start_date    end_date    booked    id    room_id

2012-07-14    2012-07-21    0       1        6
2012-07-21    2012-07-28    0       2        6
2012-07-28    2012-08-04    1       3        6
2012-08-04    2012-08-11    0       4        6

What I’d like to do is be able to get a result set that gives me one row per X weeks of consecutive unbooked dates, within a date range.

So, for 2 week blocks starting on the 14th of July and using the above table data, I would expect the following:

start_date    end_date    booked
2012-07-14    2012-07-28    0

The second block of 2 weeks would not be returned as one of the component weeks is booked.

Here are a few ideas I’ve tried already:

SELECT 
    MIN(start_date) AS start_date_min,
    MAX(end_date) AS end_date_max,
    CAST(GROUP_CONCAT(id) AS CHAR) AS ids,
    SUM(booked) AS booked
FROM 
    available_dates
WHERE
    (start_date>=20120714 AND end_date<=DATE_ADD(20120714, INTERVAL 14 DAY))
GROUP BY
    room_id
HAVING
    end_date_max=DATE_ADD(20120714, INTERVAL 14 DAY)

This gets me part of the way, however doesn’t get me the consecutive results – that is the important part. It also only returns a single result (probably because of the HAVING clause) when I widen the test data.

Can anyone point me in the right direction?

Answer 1

If you have a calendar or a numbers table:

CREATE TABLE num
( i INT NOT NULL
, PRIMARY KEY (i)
) ;

INSERT INTO num 
  (i) 
VALUES
  (0), (1), (2), ..., (1000) ;

You could use something like this:

SELECT 
    avail.room_id,
    MIN(avail.start_date) AS start_date_min,
    MAX(avail.end_date) AS end_date_max,
    CAST(GROUP_CONCAT(avail.id) AS CHAR) AS ids,
    SUM(avail.booked) AS booked
FROM 
    available_dates AS avail
  CROSS JOIN
    ( SELECT DATE('2012-07-14') AS start_date_check
           , 52                 AS max_week_check
    ) AS param
  JOIN
    num
      ON  avail.start_date = param.start_date_check + INTERVAL num.i WEEK
      AND num.i < param.max_week_check
WHERE
    avail.booked = 0
GROUP BY
    avail.room_id,
    ( num.i / 2 )        
HAVING
    COUNT(*) = 2

You could also have this:

WHERE
    1 =1                         --- no WHERE condition
GROUP BY
    avail.room_id,
    ( num.i / 2 )        
HAVING                           --- and optionally
    SUM(avail.booked) = 0        --- this