Re: Whither 1:1?

On Fri, Jun 1, 2018 at 12:52 PM, Guyren Howe <guyren(at)gmail(dot)com> wrote:

> It’s come to my attention that what seems an obvious and useful database
> design pattern — 1:1 relations between tables by having a shared primary
> key — is hardly discussed or used.
>
> It would seem to be a very simple pattern, and useful to avoid storing
> nulls or for groups of fields that tend to be used together.
>
> Thoughts? Is there some downside I can’t see?
>

You will get a benefit in terms of space only if the optional fields in the
second table exist in a reduced number of instances - and the second table
is significantly wider. This can make a difference on big tables but this
gain may be offset by the cost of the join. In this perspective, I don't
think that there is a clear benefit or drawback: it should be evaluated on
a case-by-case basis.

Olivier Gautherot