Обсуждение: Need help with a college SQL exam question...

Hi everyone,

Its coming close to my January examinations, and
while revising I got stuck in the follwing question.
I literally spent hours trying to solve it but I
just can't :(

Consider the folowing relations; (where the * means
primary key)

The "Car Rental" database
-------------------------

customer(*cust_num*,cust_name)
hire(*car_reg*,*cust_num*,*hire_date*)
shop(*outlet_code*,address)
car_model(*model*,make,num_seats,max_speed)
car(*car reg*,model,year, outlet_code)

And the question is;
Using SQL (using SELECT, FROM, WHERE, GROUP BY, COUNT(*), etc..) write a query
to list the names of customers who have borrowed cars made by every maker.

Thats it! Hard or what?

Any help greatly apreciated

"dejauser":

> Its coming close to my January examinations, and
> while revising I got stuck in the follwing question.
> I literally spent hours trying to solve it but I
> just can't :(

hmmm ... I don't think it's according to the honor code to ask us to
help with your exams.  ;-)

> And the question is;
> Using SQL (using SELECT, FROM, WHERE, GROUP BY, COUNT(*), etc..)
> write a query
> to list the names of customers who have borrowed cars made by every
> maker.

It's doable.  Just think "nested subselects" and heavy use of the HAVING
clause.  They're also screwing with you by providing an irrelevant table
(shop) and not providing a relevant table (makers).  If I was the
professor, I'd give the question writer a D+ for database design ...

-Josh

______AGLIO DATABASE SOLUTIONS___________________________                                      Josh Berkus Complete
informationtechnology      josh@agliodbs.com  and data management solutions       (415) 565-7293 for law firms, small
businesses       fax 621-2533   and non-profit organizations.      San Francisco
 

>>>>> "Josh" == Josh Berkus <josh@agliodbs.com> writes:
   Josh> It's  doable.  Just think "nested subselects"  and heavy use   Josh> of  the HAVING  clause.  They're also
screwingwith  you by   Josh>  providing an irrelevant  table (shop)  and not  providing a   Josh> relevant table
(makers). If I was the professor, I'd give   Josh> the question writer a D+ for database design ...
 

I would treat the table car_model as providing a complete list of
makes as well, i.e., "select distinct make from car_model" provides a
list of all car makes (from which the customer can borrow).

I'd agree that the database *should* have a makers table to constrain
the values of that column.  A real-life database without it is prone
to *lots* of data entry errors (let's see, should I put in GM, Chevy
or Chevrolet?).

roland
--            PGP Key ID: 66 BC 3B CD
Roland B. Roberts, PhD                             RL Enterprises
roland@rlenter.com                     76-15 113th Street, Apt 3B
roland@astrofoto.org                       Forest Hills, NY 11375

Hi,

Nice question.... I made a nice query that'll get you the result. I will not give
you the code because: 1. it's your exam, 2. I think It has some "rough edges" and
I don't want you to get the blame of my "edges" :-)

I'll give you a narrative version:

1. I'm counting the number of distinct makes...
2. I'm counting the number of distinct makes every customer has ever used (join,
join, join!) and compare that number to the result of #1

This of course happens in subqueries. I do not use HAVINGs though...
And on the design of the exam-database; lousy.

Succes,
A. Prins.

"dejauser2001@yahoo.co.uk" schreef:

> Hi everyone,
>
> Its coming close to my January examinations, and
> while revising I got stuck in the follwing question.
> I literally spent hours trying to solve it but I
> just can't :(
>
> Consider the folowing relations; (where the * means
> primary key)
>
> The "Car Rental" database
> -------------------------
>
> customer(*cust_num*,cust_name)
> hire(*car_reg*,*cust_num*,*hire_date*)
> shop(*outlet_code*,address)
> car_model(*model*,make,num_seats,max_speed)
> car(*car reg*,model,year, outlet_code)
>
> And the question is;
> Using SQL (using SELECT, FROM, WHERE, GROUP BY, COUNT(*), etc..) write a query
> to list the names of customers who have borrowed cars made by every maker.
>
> Thats it! Hard or what?
>
> Any help greatly apreciated