two date columns and one date range , typical query? - mysql

Question

I have a table
tbl_charge
id hotel_id start_date end_date charge_per_day ( in $)
1 6 2012-02-15 2010-02-15 20
2 6 2012-02-16 2010-02-18 30
4 6 2012-02-20 2010-02-25 50
Note: if any date is not in the table then we set 25$ for each days (i.e. default charge)
now if someone wants to book a hotel from 2012-02-15 to 2012-02-22 , then I want to calculate the total charges for dates
Date : 15+16+17+18+19+20+21+22
Charge : 20+30+30+30+25+50+50+50 = 285$
what i have done so far:
this query returns all rows successfully
SELECT * FROM `tbl_charge` WHERE
start_date BETWEEN '2012-02-15' AND '2012-02-22' OR
end_date BETWEEN '2012-02-15' AND '2012-02-22' OR
( start_date <'2012-02-15' AND end_date > '2012-02-22')
HAVING property_id=6
it returns all necessary rows but how do I sum the charges??
is ther any way to count days between given date range like last row is 20 -25 but i want only upto 22 then it return 3 days and we multiply charges by 3
is it good to create procedure for this or use simple query

Answer 1

I think this will do the trick:
select sum(DayDifference * charge_per_day) +
(RealDayDifference - sum(DayDifference)) * 25 as TotalPerPeriod
from (
select charge_per_day, datediff(
least(end_date, '2012-02-22'),
greatest(start_date, '2012-02-15')) + 1 as DayDifference,
datediff('2012-02-22', '2012-02-15') + 1 as RealDayDifference
from t1
where
((start_date between '2012-02-15' and '2012-02-22') or
(end_date between '2012-02-15' and '2012-02-22') or
(start_date < '2012-02-15' and end_date > '2012-02-22'))
and hotel_id=6
) S1

Answer 2

I've had to solve this same issue previously and it's a fun one, however since then I've learnt some better methods. At the time I believe I created a procedure or function to loop over the requested dates and return a price.
To return the required rows, you can simply select using the upper and lower limits. You can do a datediff within the select criteria to return the number of iterations of each to apply.
If all you are ultimately looking for is a single price I would advise combining this logic into a function
I've assumed a second table, tbh_hotel with id (int PK == hotel_id) and default_charge (int) with row (id=6,default_charge=20)
Further assumptions are that where your dates are "2010" you meant them to be "2012", and that this is for someone that is checking in in the 15th, and checking out on the 22nd (and so needs a hotel for 15th, 16th, 17th, 18th, 19th, 20th, 21st, 7 nights). I will also assume that you have logic in place that prevents the date ranges overlapping, so that there are no 2 rows in tbl_charge which match the date 14th Feb 2012 (for example)
So to get this started, a query to select the applicable rows
SELECT
*
FROM tbl_charge AS c
WHERE
(
c.end_date >= '2012-02-15'
OR
c.start_date < '2012-02-22'
)
This is pretty much what you have already, so now will add in some more fields to get the information for how many days each rule is applied for.
SET #StartDate = '2012-02-15';
SET #EndDate = SUBDATE('2012-02-22',1);
SELECT
c.id,
c.start_date,
c.end_date,
c.charge_per_day,
DATEDIFF(IF(c.end_date>#EndDate,#EndDate,c.end_date),SUBDATE(IF(c.start_date<#StartDate,#StartDate,c.start_date),1)) AS quantityOfThisRate
FROM tbl_charge AS c
WHERE c.end_date >=#StartDate OR c.start_date < #EndDate
I am SUBDATEing the end date, because if you check out on the 22nd, your final checkin date is the 21st. I am SUBDATING the start date on each DATEDIFF because if you are staying on 15th -> 16th, the subdate on END DATE makes this 15th-15th, and so this SUBDATE makes it get 14th-15th to return the correct value of 1. Output now looks a bit like this
id start_date end_date price quantityAtThisRate
1 2012-02-10 2012-02-15 20 1
2 2012-02-16 2012-02-18 30 3
3 2012-02-20 2012-02-29 50 2
So moving on I'll put this into a subquery and combine tbl_hotel to get a default charge
SET #StartDate = '2012-02-15';
SET #EndDate = SUBDATE('2012-02-22',1);
SET #NumberOfNights = DATEDIFF(ADDDATE(#EndDate,1),#StartDate);
SET #HotelID = 6;
SELECT
SUM(specificDates.charge_per_day*specificDates.quantityAtThisRate) AS specificCharges,
#NumberOfNights-SUM(specificDates.quantityAtThisRate) AS daysAtDefault,
h.default_charge * (#NumberOfNights-SUM(specificDates.quantityAtThisRate)) AS defaultCharges
FROM tbl_hotel AS h
INNER JOIN
(
SELECT
c.charge_per_day,
DATEDIFF(IF(c.end_date>#EndDate,#EndDate,c.end_date),SUBDATE(IF(c.start_date<#StartDate,#StartDate,c.start_date),1)) AS quantityAtThisRate
FROM tbl_charge AS c
WHERE (c.end_date >=#StartDate OR c.start_date < #EndDate) AND c.hotel_id = #HotelID
) AS specificDates
WHERE h.id = #HotelID
Realistically a single query will get rather .... complex so I'd settle at a stored procedure relying on the logic above (as if there are no specific rules the above query will return null due to the inner join)
Hope this is of help