Re: Character string relation and functional dependencies

From: V.J. Kumar <vjkmail_at_gmail.com>
Date: Tue, 11 Dec 2007 22:27:48 +0100 (CET)
Message-ID: <Xns9A03A7900AB6Cvdghher@194.177.96.26>

Tegiri Nenashi <TegiriNenashi_at_gmail.com> wrote in news:38860a21-e69a- 46a4-a798-cc16dde1c4a7_at_e10g2000prf.googlegroups.com:

> On Dec 11, 12:37 pm, Tegiri Nenashi <TegiriNena..._at_gmail.com> wrote:

>> Well, in traditional databases index structures are auxiliary.
>> Likewise, I would like to keep functions hidden. After all there is
>> one relation
>>
>> x + y = z
>>
>> but there are three functions that can index it.

>
> Let me elaborate a little more. Suppose we are asked to evaluate the
> query
>
> x + y = z /\ x=1 /\ z=4
>
> there is no functions there. As usual optimizer engine starts
> enumerating and costing every join permutation. It would find out that
> the execution below has a finite cost:
>
> 1. Evaluate x=1
> 2. Evaluate z=4
> 3. Build a Cartesian product result
> 4. Join with the relation x + y = z using the index (x,z)->z-x

What would your optimizer do in the following case:

x^2 + y^2 + z^2 =u^2 /\ u=25

? Received on Tue Dec 11 2007 - 15:27:48 CST