Query: Calculate average price of stay depending on dates - php

Question

Hello all,
I need to create a query for house search, that would match in database user entered data: date when they want to move in and leave, number of people they have in group and price per night.
Lets say user searched for house:
dates: from 2011-01-15 to 2011-03-01 (see on picture period A1C1), for 3 people, and he is willing to spend from $90 to $125 dollars per night.
This is my manual calculations for this search:
dates available in database
total number of dates user wants to stay is: 44 days
price for the first period 2011-01-15 to 2011-01-25 is 10 days * $100 = $1000
price for the second period 2011-01-25 to 2011-02-14 is 20 days * $120 = $2400
price for the third period 2011-02-14 to 2011-03-01 is 14 days * $140 = $1960
total average price per night = 1000 + 2400 + 1960 / 44 = $121.8
price and number of people matches user input, so we display this house
If you merge dates and calculate average price per night for the given period, search script should match array of data provided above.
My question is this: How my query should look like to calculate quickly if user data matches records in database.
I was thinking about using SQL DATEDIFF function and then multiply by price ... etc but it looks to me pretty complex.
I will appreciate any advice.
Thank you
UPDATE
Here is my database schema:
Table "apt_search_periods" which stores all merged dates (continuous dates from availability table)
+-----------+------------+------------+-----------+--------------+--------+
| period_id | start_date | end_date | rental_id | nb_of_people | merged |
+-----------+------------+------------+-----------+--------------+--------+
| 21 | 2011-03-31 | 2012-03-31 | 548 | 4 | y |
+-----------+------------+------------+-----------+--------------+--------+
Table "apt_search_periods_avail" linking merged dates with availability table
+----+-----------+-----------------+
| id | period_id | availability_id |
+----+-----------+-----------------+
| 21 | 21 | 20953 |
| 22 | 21 | 20952 |
| 23 | 21 | 4033 |
+----+-----------+-----------------+
Table "availability" with expanded dates and prices
+-------+-----------+------------+------------+--------------+--------------+
| id | rental_id | start_date | end_date | nb_of_people | rent_per_day |
+-------+-----------+------------+------------+--------------+--------------+
| 20952 | 548 | 2011-03-31 | 2011-07-01 | 4 | 575 |
| 4033 | 548 | 2011-07-01 | 2011-09-01 | 4 | 680 |
| 20953 | 548 | 2011-09-01 | 2012-03-31 | 4 | 575 |
+-------+-----------+------------+------------+--------------+--------------+

Answer 1

Following should get you started.
Note that the only difference is that the third period comprises 15 days io 14 according to DATEDIFF.
SQL Statement
;WITH q AS (
/* Kick of with the record where startdate < input < enddate */
SELECT date_start
, date_end
FROM #HouseSearch
WHERE date_start <= #date_start
AND date_end >= #date_start
AND nb_people >= #nb_people -- Only when number of people is adequate
UNION ALL
SELECT q.date_start
, hs.date_end
FROM q
INNER JOIN #HouseSearch hs ON hs.date_start = q.date_end
WHERE nb_people >= #nb_people -- Only when number of people is adequate
)
SELECT *
FROM (
-- Only return result if sequence exists between date range
SELECT date_start = MIN(date_start)
, date_end = MAX(date_end)
FROM q
WHERE date_end >= #date_end
) datetimerange
-- Calculate the average price
CROSS APPLY (
SELECT [AveragePrice] = SUM(price / DATEDIFF(dd, #date_start, #date_end))
FROM (
-- Price for all records where date_end <= #date_end
SELECT [price] =
CASE WHEN #date_start < date_start
THEN DATEDIFF(dd, date_start, date_end) * price
ELSE DATEDIFF(dd, #date_start, date_end) * price
END
FROM #HouseSearch
WHERE #date_end > date_end
UNION ALL
-- Price of remaining records where date_end >= #date_end
SELECT DATEDIFF(dd, date_start, #date_end) * price
FROM #HouseSearch
WHERE #date_end between date_start AND date_end
) prices
) price
WHERE date_start IS NOT NULL
Test data
DECLARE #HouseSearch TABLE (
date_start DATE
, date_end DATE
, nb_people INTEGER
, price FLOAT
)
INSERT INTO #HouseSearch VALUES
('2011-01-01', '2011-01-25', 4, 100)
, ('2011-01-25', '2011-02-14', 3, 120)
, ('2011-02-14', '2011-03-12', 3, 140)
, ('2011-03-12', '2011-04-10', 3, 100)
DECLARE #date_start DATE = '2011-01-15'
DECLARE #date_end DATE = '2011-03-01'
DECLARE #nb_people INTEGER = 3
DECLARE #price_low FLOAT = 90
DECLARE #price_high FLOAT = 15