Re: Teach SELECT DISTINCT first!

Mikito Harakiri wrote:

>> OK here's a pathological example: Define a function f on the 
>> integers by: f(i) = i  (if Fermat's Last Theorem is true
 >>                   = 0  (if Fermat's Last Theorem is false

I'm sure you could expand it out in terms of arithmetic operations and elementary functions. It might be very long though...

> CAS have their own problems even within practical realm of
> closed-form expressions, there is no need to go as far as FLT. The
> idea is however, that in vast majority of the cases CAS does an
> excellent work.

OK so say for example I do "SELECT i from R WHERE i*i < 0" where i is an integer column, then the DBMS engine should know that the square of an integer is never less than zero?

>> Now functions are actually special cases of (mathematical) 
>> relations. So maybe a relational system could think of them in this
>>  way and access them as logical (DBMS) relations. Whether they are
>>  physically implemented as an actual table or not would be up to
>> the optimizer. For example say you define a complicated function on
>>  the integers. It might be best for the DBMS to store a table that
>>  pre-calculates this.

Maybe the DBMS could store statistics about what actual ranges are used for a function in practice and physically store them which would help in 99% of cases?

>> For non-integer domains you might have more problems though. But 
>> then you've already got problems with rounding etc. where two 
>> decimals may be different theoretically but the same according to 
>> the DBMS.

Yes, I guess the problem is it's very complicated to write just a plain DBMS, let alone one with fancy optimizations, unlimited precision and computer algebra systems etc. built in.

Paul. Received on Wed Apr 28 2004 - 01:48:32 CEST