# 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_at_194.177.96.26>

> Let me elaborate a little more. Suppose we are asked to evaluate the

Date: Tue, 11 Dec 2007 22:27:48 +0100 (CET)

Message-ID: <Xns9A03A7900AB6Cvdghher_at_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 - 22:27:48 CET