Jeffrey Tenny <jeffrey.tenny@comcast.net> writes:
> What are the performance tradeoffs (storage space, query speed) of using
> a NULL enabled column versus a NOT-NULL column with a sentinel integer
> value?
> Not that it matters, but in the event where the column values matter,
> the numberic value is a foreign key. Advice on that welcome too.
In that case you want to use NULL, because the foreign key mechanism
will understand that there's no reference implied. With a sentinel
value you'd have to have a dummy row in the master table --- which will
cause you enough semantic headaches that you don't want to go there.
The performance difference could go either way depending on a lot of
other details, but it will be insignificant in any case. Don't screw up
your database semantics for it.
regards, tom lane
