Re: design of tables for sparse data

Fernando Hevia schrieb:
>> --- Andreas Wrote: ---
>> ...
>>
>> MY QUESTIONS:
>>
>
> Your questions have a strong "home-work" look.
>

Yes but I didn't want to bother everyone with my project's details.
It's more like a CRM.
Up until now I just tried to manage somehow with the sql basics and now
I like to get better.
One interesting thing are crosstabs because I could use them in the
reporting module.

I used this schoolbook scenario because it's such an easy example. ;)

>> 1) How would I SELECT a report that looks like the first version of
>> the pupil table out of the 3 table design?
>> There must be a nontrivial SELECT statement that combines all 3 tables.
>>
>
> You should check out the JOIN clause in select statements.
> Simple example:
>
> Select t1.col1, t2.col1, t2.col2
> >from t1 inner join t2 b on (t1.col1 = t2.col1)
>

A simple JOIN won't do the trick.
That would give me something like:
(42, Frank Miller, Maths)
(42, Frank Miller, English)
(42, Frank Miller, Sports)
(43, Suzy Smith, Maths)
(43, Suzy Smith, History)

But I want it turned around and a bit interpreted like:

Column heads = (ID, Name, Maths, English, Sports, History)
(42, Frank Miller, yes, yes, yes, no )
(43, Suzy Smith, yes, no, no, yes)

Regards
Andreas