Re: Add numeric_trim(numeric)

2016-01-07 1:11 GMT+01:00 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:

> Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> writes:
> > On 6 January 2016 at 20:09, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> >> On Wed, Jan 6, 2016 at 10:21 AM, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>
> wrote:
> >>> It seems like a useful function to have, but perhaps it should just be
> >>> called trim() rather than numeric_trim(), for consistency with the
> >>> names of the other numeric functions, which don't start with
> >>> "numeric_".
>
> >> That wouldn't work in this case, because we have hard-coded parser
> >> productions for TRIM().
>
> Does it have to be called TRIM()? After looking at the spec for it
> I'd think rtrim() is the more correct analogy.
>
> Also worth noting is that those hard-wired parser productions aren't
> as hard-wired as all that.
>
> regression=# select trim(43.5);
> ERROR: function pg_catalog.btrim(numeric) does not exist
>
> If we wanted to call the function btrim() underneath, this would
> Just Work. However, to alleviate confusion, it might be better
> if we altered the grammar productions to output "trim" not "btrim"
> for the not-LEADING-or-TRAILING cases, and of course renamed the
> relevant string functions to match.
>
> A different approach is that I'm not real sure why we want a function
> that returns a modified numeric value at all. To the extent I understood
> Marko's original use case, it seems like what you'd invariably do with the
> result is extract its scale(). Why not skip the middleman and define a
> function named something like minscale() or leastscale(), which returns an
> int that is the smallest scale that would not drop data? (If you actually
> did want the modified numeric value, you could use round(x, minscale(x))
> to get it.)
>

A example "round(x, minscale(x))" looks nice, but there can be a
performance issues - you have to unpack varlena 2x

I'll try to some performance tests

Regards

Pavel

> regards, tom lane
>