Query: Calculate average price of stay depending on dates

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开发者_如何转开发 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 |
+-------+-----------+------------+------------+--------------+--------------+

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