MySQL Calculate minimum price of a service with varying starting time - mysql

Question

Suppose I have a table like this:
Prices
-----------------------------------------------------------
| service_id | starting_time | ending_time | price_per_hour |
-----------------------------------------------------------
| 1 | 08:00:00 | 10:00:00 | 90 |
-----------------------------------------------------------
| 1 | 10:00:00 | 11:00:00 | 50 |
-----------------------------------------------------------
| 1 | 11:00:00 | 15:00:00 | 80 |
-----------------------------------------------------------
Now a user of my web page wants to find service providers with lowest price. They tell me starting time of the service, duration and (here's the tricky part) tolerance for the starting time. Say, service should start at 10am, should last 2 hours but they are willing to come one hour earlier or later (+/- 1 hour to starting time).
I cannot seem to come up with an idea of one query to get me the lowest possible price, depending if the service starts at 9am, 10am or 11am. starting time tolerance may vary. It's easy, if there's no tolerance, you just select all rows from prices that apply to the service time, calculate their share in price and then sum the subquery. But how do I introduce the variable starting time factor into that?
This is a simplified query to calculate price knowing exact starting point of the service. :service_start and service_end are placeholders.
SELECT SUM(t1.price) FROM
(SELECT price_per_hour * TIME_TO_SEC( TIMEDIFF( IF(ending_time < :service_end,
ending_time, :service_end), IF(starting_time < :service_start, :service_start,
starting_time) ) ) / 3600 AS price FROM prices WHERE service_id = 1 AND NOT
(starting_time >= :service_end OR ending_time <= :service_start)) AS t1
And now I have no idea where to go on from here. How to introduce variability of service starting time.
EDIT:
Ok, I think I was too lazy to think deeper about that before. I believe it can't be done using MySQL. I've broken it down to mathematical equasions that would solve it and I believe it's not something you can implement in MySQL (two equasions with many variables). I think it's going to have to be some brute force calculations on PHP side to get what I want.
In this instance I would want to minimise x * 90 + y * 50 + z * 80, where x, y, z is number of hours taken from each price range given some conditions, such as x,y,z%0,5 = 0 (half an hour step), x+y+z = 2, etc.
EDIT 2:
I'll describe the issue in more detail, as it seems I wansn't specific enough:
I have three tables that are relevant to this issue:
services
-----------------------------------------------------------------------------------------------
| service_id | service_type_id | provider_id | name | starting_time | ending_time |
-----------------------------------------------------------------------------------------------
| 2 | 1 | 3 | 2014-02-07 08:00:00 | 2014-02-07 23:00:00 |
-----------------------------------------------------------------------------------------------
prices (more a price list)
------------------------------------------------------------------------------
| service_type_id | provider_id | starting_time | ending_time | price_per_hour |
------------------------------------------------------------------------------
| 1 | 3 | 08:00:00 | 10:00:00 | 90 |
------------------------------------------------------------------------------
| 1 | 3 | 10:00:00 | 11:00:00 | 50 |
------------------------------------------------------------------------------
| 1 | 3 | 11:00:00 | 15:00:00 | 80 |
------------------------------------------------------------------------------
| 1 | 3 | 15:00:00 | 23:00:00 | 70 |
------------------------------------------------------------------------------
service_slots
-----------------------------------------------------------------------------------
| service_slot_id | service_id | starting_time | ending_time | booked |
-----------------------------------------------------------------------------------
| 1 | 2 | 2014-02-07 08:00:00 | 2014-02-07 09:00:00 | 1 |
| 2 | 2 | 2014-02-07 09:00:00 | 2014-02-07 17:00:00 | 0 |
| 3 | 2 | 2014-02-07 17:00:00 | 2014-02-07 19:00:00 | 1 |
| 4 | 2 | 2014-02-07 19:00:00 | 2014-02-07 21:00:00 | 1 |
| 5 | 2 | 2014-02-07 21:00:00 | 2014-02-07 23:00:00 | 0 |
-----------------------------------------------------------------------------------
The first table contains service schedule of a provider. The provider says they're offering the service between 8am and 11pm. You can book as much time off that service as you want (think tennis court booking).
They also have a pricing for those services. This pricing says that every day (during price list validity), the service costs this and that between this and that hour. You can book the service across price ranges. That is, if the price list says that the service costs 90 between 8am and 10am and 50 between 10am and 11am, it's perfectly fine for you to book between 9 and 11. Then two price ranges apply to your booking.
The third table holds information on which chunk (slot) of a particular service has been booked.
What I do is first query service_slots for available chunks then I need to get the price for the entire duration of the chunk, knowing that price may change in the middle of the chunk's duration.
I hope I mad myself more clear this time :)

Answer 1

HEAVILY EDITED, SO OLD POST IS GONE!
First, check out my codes.
My test table :
CREATE TABLE IF NOT EXISTS price(
id INT(20) NOT NULL AUTO_INCREMENT PRIMARY KEY,
pid INT(20) NOT NULL,
staring_time DATETIME,
ending_time DATETIME,
price INT(20) NOT NULL
);
And the queries:
SET #start_pref = '2014-02-07 02:00:00';
SET #end_pref = '2014-02-07 04:00:00';
SELECT
*,
(
SELECT id
FROM price
WHERE
pid = p.pid AND
starting_time <= #start_pref AND
ending_time > #start_pref
) AS id_first,
(
SELECT id
FROM price
WHERE
pid = p.pid AND
ending_time >= #end_pref AND
starting_time < #end_pref
) AS id_last,
(
SELECT IF(
id_first = id_last,
(
SELECT HOUR(TIMEDIFF(#end_pref, #start_pref)*price)
FROM price
WHERE id = id_first AND pid = p.pid
),
(
(
SELECT HOUR(TIMEDIFF(ending_time, #start_pref)*price)
FROM price
WHERE id = id_first AND pid = p.pid
) + (
SELECT HOUR(TIMEDIFF(#end_pref, starting_time)*price)
FROM price
WHERE id = id_last AND pid = p.pid
)
)
) FROM price WHERE pid = p.pid AND id = id_first
) AS total
FROM price p
WHERE
starting_time <= #start_pref AND #start_pref < ending_time
ORDER BY total ASC;
This only works for, when #start_pref and #end_pref covers 1 - 2 successive time-sched.
However, it does not work for, when the pref time covers more than 2 records.
Example:
Starting pref time: 1am
Ending pref time: 5am
For one specific provider
1am - 2am - $10
2am - 3am - $20
4am - 5am - $30
This is because I didn't think of it beforehand when I started and finished my query.
Now if it is two or more, you'd need more subquery to find those id then add them on my SELECT IF( subquery.
Also, notice how I have/added the column id? So that I can tell easily if that id belongs to the same pid on the current query.
PID is Provider ID.
The whole sql script.