Re: Character string relation and functional dependencies

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