Re: New feature: accumulative functions.

=?ISO-8859-2?Q?pasman_pasma=F1ski?= <pasman(dot)p(at)gmail(dot)com> writes:
> I found second use case. Look at expression:
> where left(str,n)='value'

> function left(str,n) increase monotonically for str and n. With this
> feature it can use index on str.

Can't get excited about that, because that only works in C locale,
and in C locale you can already get the same result with
WHERE str LIKE '...%'

Also, I think you just moved the goalposts quite a bit by introducing
multiple-argument functions into the proposed feature. That's going
to add even more complexity, for instance there would need to be a way
to specify which argument(s) the function was monotonic in. The C
versus not-C locale aspect also shows that for textual arguments,
it might matter which locale you're talking about.

In short, this is looking awfully complicated, and I gauge the probable
level of interest by the fact that you're the first person to ask for it
in more than a dozen years of Postgres development.

regards, tom lane