Shantanu's Blog

Corporate Consultant

April 07, 2006

 

MySQL Case Study - 116

I'm a bit stomped with something I would like to do in mysql, but not sure how I should do it.
Perhaps it's not even possible, I'll try to explain.
I have two tables, Rents and Vechicules.
In the Rents table I have these fields, CustomerId, startdate, enddate, vechicleId as int, date, date, int resp.
The Vechicules table contains the fields VechiculeId and licenseplate.

So there's a link from the Rents to the vechicules table with vechiculeId.
With this i could see which customer has which car in a certain start to end date,
but also, because there's a carpooling scheme and insurances we can have 2 or more customers renting the same car.

And I want to be able to search in the Rents table with the Customer id, a start date and an endate and return all the rows where that certain customer is the sole renter.
No with the carpool we would have in the Rents table:
2 - 04/04/06 - 04/11/06 - 6
3 - 04/04/06 - 04/31/06 - 6


So customers 2 and 3 are carpooling from 04/04 to 04/11 and then after that customer 3 is the sole renter from 04/15 until 04/31.

Long dragged out question, can someone help out with this query? I really don't know whether it even possible with mysql.

http://forums.mysql.com/read.php?10,81050,81050#msg-81050

Comments:
Here's a solution that seems to work. This sort of problem isn't easy.

CREATE TABLE `rents` (
`customerid` int(11) default NULL,
`startdate` date default NULL,
`enddate` date default NULL,
`vehicleid` int(11) default NULL
)

INSERT INTO rents VALUES
(2, '2006-04-04', '2006-04-11', 6),
(3, '2006-04-06', '2006-04-30', 6),
(4, '2006-04-04', '2006-04-11', 8);

select r2.customerid, r2.vehicleid, r2.startdate as s2, r1.startdate as s1
from rents as r1 inner join rents as r2
on (r1.vehicleid = r2.vehicleid and r1.customerid <> r2.customerid
and (r1.startdate > r2.startdate and r1.startdate <= r2.enddate))
union all
select r2.customerid, r2.vehicleid, r1.enddate as s2, r2.enddate as s1
from rents as r1 inner join rents as r2
on (r1.vehicleid = r2.vehicleid and r1.customerid <> r2.customerid
and (r1.enddate < r2.enddate and r1.enddate >= r2.startdate))
union all
select r1.customerid, r1.vehicleid, r1.startdate, r1.enddate
from rents as r1 left outer join rents as r2
on (r1.vehicleid = r2.vehicleid and r1.customerid <> r2.customerid
and (r1.startdate between r2.startdate and r2.enddate or r1.enddate between r2.startdate and r2.enddate))
where r2.customerid is null
 
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