Re: Getting a leading zero on negative intervals with to_char?

On Thu, Sep 20, 2012 at 09:42:33AM +0800, Craig Ringer wrote:
> Hi all
>
> I'm wondering if there's any way to convince `to_char` to add a leading zero to
> the hours in negative intervals. The current behaviour feels wrong, in that
> FMHH24:MM and HH24:MM produce the same output for negative intervals:
>
> regress=# WITH x(i) AS (VALUES (INTERVAL '9:00'),(INTERVAL '-9:00'),
> (INTERVAL '11:00'),(INTERVAL '-11:00'),(INTERVAL '101:00'),(INTERVAL
> '-101:00') )
> SELECT i as "interval", to_char(i,'HH24:MM') as "HH24:MM", to_char
> (i,'FMHH24:MM') AS "FMHH24:MM" FROM x;
> interval | HH24:MM | FMHH24:MM
> ------------+---------+-----------
> 09:00:00 | 09:00 | 9:00
> -09:00:00 | -9:00 | -9:00
> 11:00:00 | 11:00 | 11:00
> -11:00:00 | -11:00 | -11:00
> 101:00:00 | 101:00 | 101:00
> -101:00:00 | -101:00 | -101:00
> (6 rows)
>
>
> I can't find any way to produce the output '-09:00' . There's no apparent way
> to add an additional width-specifier. HH24 is clearly not constrained to be 2
> digits wide, since "-11" and "101" and "-101" are all output by "HH24". It
> seems like "-9" should be "-09" with the HH24 specifier, and "-9" with the
> "FMHH24" specifier.
>
> Opinions?
>
> Unless I'm doing something woefully wrong, Oracle compatibility doesn't seem to
> be an issue because we format intervals wildly differently to Oracle anyway:
>
> http://sqlfiddle.com/#!4/d41d8/2751
>
> and it looks like Oracle handling of intervals isn't much like Pg anyway:
>
> http://stackoverflow.com/questions/970249/format-interval-with-to-char
>
>
> Arose from trying to find a non-ugly solution to this SO post:
>
> http://stackoverflow.com/questions/12335438/server-timezone-offset-value/
> 12338490#12338490

[This is for 9.6.]

I looked over this report from 2012, and the behavior still exists. I
think we have not seen more reports about this because negative
hours/years is not something people regularly use, but you found a need
for it.

I think the big question is whether YYYY (4) or HH24 (2) represents
characters. or digits for zero-padding. printf() assumes it is
characters, e.g. %02d outputs "-2" not "-02", but I think our API
suggests it is digits, meaning the minus sign is not part of the
specific length, i.e. a minus sign is not a digit.

I have developed the attached unified-diff patch which changes the
behavior to not consider the negative sign as a digit in all the places
I thought it was reasonable.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ Everyone has their own god. +