Re: converting between infinity timestamp and float8 (epoch)

On Tue, Dec 27, 2011 at 10:41 AM, Phil Sorber <phil(at)omniti(dot)com> wrote:
> So first off some ground work:
>
> postgres=# select 'infinity'::timestamp;
>  timestamp
> -----------
>  infinity
> (1 row)
>
> postgres=# select 'infinity'::float8;
>  float8
> ----------
>  Infinity
> (1 row)
>
> Establishing that we do in fact have an infinity value for both the
> timestamp type and the double precision type.
>
> If I try to convert between them:
>
> postgres=# select to_timestamp('infinity'::float8);
> ERROR:  timestamp out of range
> CONTEXT:  SQL function "to_timestamp" statement 1
>
> Ok, so that didn't work. Maybe there is something in the SQL standard
> stating that this should not be possible? At least it reports an
> error.
>
> However, if I try:
>
> postgres=# select extract(epoch from 'infinity'::timestamp);
>  date_part
> -----------
>         0
> (1 row)
>
> This seems busted. Even if we were to consider 0 to be a special
> "error value" it would lead to things like this:
>
> postgres=# select to_timestamp(extract(epoch from 'infinity'::timestamp));
>      to_timestamp
> ------------------------
>  1969-12-31 19:00:00-05
> (1 row)
>
> So I think the second form (extract) should return an error, or better
> yet, they should both do the intuitive thing that is to return
> 'infinity' of the appropriate type.
>
> Thoughts?

My search foo failed me. Someone just pointed me to a similar
conversation from some months ago:
http://archives.postgresql.org/pgsql-hackers/2011-07/msg00677.php

I would propose that since we can't know the hour or minute of
infinity that we should return null for those. I think NaN would be
wrong because it is a real number, it's just unknown. If we can just
pass infinity through the function, I think we should.