Re: Infinities in type numeric - Mailing list pgsql-hackers

From Tom Lane
Subject Re: Infinities in type numeric
Date
Msg-id 3362332.1594917787@sss.pgh.pa.us
Whole thread Raw
In response to Re: Infinities in type numeric  (Dean Rasheed <dean.a.rasheed@gmail.com>)
Responses Re: Infinities in type numeric
List pgsql-hackers
Dean Rasheed <dean.a.rasheed@gmail.com> writes:
> I had a look at this, and I think it's mostly in good shape. It looks
> like everything from the first message in this thread has been
> resolved, except I don't know about the jsonpath stuff, because I
> haven't been following that.

Thanks for the careful review!  Yeah, Alexander fixed the jsonpath
stuff at df646509f, so I think all my original concerns are cleared,
other than the question of whether to invent isfinite() and isnan()
SQL functions.  That seems like follow-on work in any case.

> 1). I don't think that the way in_range() handles infinities is quite
> right. For example:

> SELECT in_range('inf'::numeric, 10::numeric, 'inf'::numeric, false, false);
>  in_range
> ----------
>  f
> (1 row)

> But I think that should return "val >= base + offset", which is "Inf
> >= Inf", which should be true.

Hmm.  I modeled the logic on the float8 in_range code, which does the
same thing:

# SELECT in_range('inf'::float8, 10::float8, 'inf'::float8, false, false);
 in_range
----------
 f
(1 row)

It does seem like this is wrong per the specification of in_range, though,
so do we have a bug to fix in the float in_range support?  If so I'd
be inclined to go correct that first and then adapt the numeric patch
to match.

> Similarly, I think this should return true:
> SELECT in_range('-inf'::numeric, 10::numeric, 'inf'::numeric, true, true);

Same comment.

> I think this could use some test coverage.

Evidently :-(

> 2). I think numeric_pg_lsn() needs updating -- this should probably be an error:

Oh, that was not there when I produced my patch.  Will cover it in the
next version.

I agree with your other comments and will update the patch.

> Finally, not really in the scope of this patch, but something I
> noticed anyway while looking at edge cases -- float and numeric handle
> NaN/0 differently:
> SELECT 'nan'::float8 / 0::float8;
> ERROR:  division by zero
> SELECT 'nan'::numeric / 0::numeric;
>  ?column?
> ----------
>       NaN

Hmm.  It seems like we generally ought to try to follow IEEE 754
for the semantics of operations on NaN, but I don't have a copy of
that spec so I'm not sure which result it specifies for this.
I agree that being inconsistent between the two types is not what
we want.

            regards, tom lane



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