Thread: BUG #17496: to_char function resets if interval exceeds 23 hours 59 minutes

The following bug has been logged on the website:

Bug reference:      17496
Logged by:          Yankz
Email address:      qubzen@gmail.com
PostgreSQL version: 13.7
Operating system:   Mac Os
Description:

to_char function resets if interval exceeds 23 hours 59 minutes found at:
https://www.postgresql.org/docs/current/functions-formatting.html#FUNCTIONS-FORMATTING-TABLE

Tested for both 13 and 14 versions. Check here:
https://dbfiddle.uk/?rdbms=postgres_14&fiddle=31f5d8b7e8dbf855e1907e6e8f01d5cf

On Tue, May 24, 2022 at 03:55:49PM -0400, Jeff Janes wrote:
> On Tue, May 24, 2022, 3:23 PM PG Bug reporting form <noreply@postgresql.org>
>> to_char function resets if interval exceeds 23 hours 59 minutes found at:
>>
>> https://www.postgresql.org/docs/current/functions-formatting.html#FUNCTIONS-FORMATTING-TABLE
>>
>> Tested for both 13 and 14 versions. Check here:
>>
>> https://dbfiddle.uk/?rdbms=postgres_14&fiddle=31f5d8b7e8dbf855e1907e6e8f01d5cf
> 
> 
> I don't see how this is a bug. You told it not to display the days or
> higher units, so it doesn't.

The documentation for this function indicates HH24 can output hour values
higher than 23∴

        <function>to_char(interval)</function> formats <literal>HH</literal> and
        <literal>HH12</literal> as shown on a 12-hour clock, for example zero hours
        and 36 hours both output as <literal>12</literal>, while <literal>HH24</literal>
        outputs the full hour value, which can exceed 23 in
        an <type>interval</type> value.

I see different results depending on how I define the interval:

    postgres=# select to_char(INTERVAL '1 day', 'HH24:MI');
     to_char 
    ---------
     00:00
    (1 row)

    postgres=# select to_char(INTERVAL '24h', 'HH24:MI');
     to_char 
    ---------
     24:00
    (1 row)

The example provided is more like the former (no hour value), because
"timestamp - timestamp" converts 24-hour intervals into days.  In general,
I agree that this probably not a bug.  You probably want to ask to_char()
to display the days as well..

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

On Tue, May 24, 2022 at 01:11:45PM -0700, Nathan Bossart wrote:
> The documentation for this function indicates HH24 can output hour values
> higher than 23∴
> 
>         <function>to_char(interval)</function> formats <literal>HH</literal> and
>         <literal>HH12</literal> as shown on a 12-hour clock, for example zero hours
>         and 36 hours both output as <literal>12</literal>, while <literal>HH24</literal>
>         outputs the full hour value, which can exceed 23 in
>         an <type>interval</type> value.
> 
> I see different results depending on how I define the interval:
> 
>     postgres=# select to_char(INTERVAL '1 day', 'HH24:MI');
>      to_char 
>     ---------
>      00:00
>     (1 row)
> 
>     postgres=# select to_char(INTERVAL '24h', 'HH24:MI');
>      to_char 
>     ---------
>      24:00
>     (1 row)
> 
> The example provided is more like the former (no hour value), because
> "timestamp - timestamp" converts 24-hour intervals into days.  In general,
> I agree that this probably not a bug.  You probably want to ask to_char()
> to display the days as well..

Well, if we did that then this would be odd:

    SELECT to_char(INTERVAL '2 day', 'DD HH24:MI');
     to_char
    ----------
     02 00:00

or this:

    SELECT to_char(INTERVAL '2 day 4 hours', 'DD HH24:MI');
     to_char
    ----------
     02 04:00
    
-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Indecision is a decision.  Inaction is an action.  Mark Batterson

At Thu, 14 Jul 2022 17:57:32 -0400, Bruce Momjian <bruce@momjian.us> wrote in 
> On Tue, May 24, 2022 at 01:11:45PM -0700, Nathan Bossart wrote:
> > The documentation for this function indicates HH24 can output hour values
> > higher than 23∴
> > 
> >         <function>to_char(interval)</function> formats <literal>HH</literal> and
> >         <literal>HH12</literal> as shown on a 12-hour clock, for example zero hours
> >         and 36 hours both output as <literal>12</literal>, while <literal>HH24</literal>
> >         outputs the full hour value, which can exceed 23 in
> >         an <type>interval</type> value.
> > 
> > I see different results depending on how I define the interval:
> > 
> >     postgres=# select to_char(INTERVAL '1 day', 'HH24:MI');
> >      to_char 
> >     ---------
> >      00:00
> >     (1 row)
> > 
> >     postgres=# select to_char(INTERVAL '24h', 'HH24:MI');
> >      to_char 
> >     ---------
> >      24:00
> >     (1 row)
> > 
> > The example provided is more like the former (no hour value), because
> > "timestamp - timestamp" converts 24-hour intervals into days.  In general,
> > I agree that this probably not a bug.  You probably want to ask to_char()
> > to display the days as well..

On the other hand, "interval + interval" doesn't convert hours into
days. I expected the math to do normalization.

select INTERVAL '1 day 15hour' + interval '2 day 15 hour';
    ?column?     
-----------------
 3 days 30:00:00

Is there any means to control over normalization?

> select normalize_interval('3 days 30:00:00'::interval, 'HH24:MI')
> 102:00
> select normalize_interval('3 days 30:00:00'::interval, 'DD HH24:MI')
> 4 04:00
> select normalize_interval('3 days 30:00:00'::interval, 'HH12:MI')
> ERROR:  hours out of range


> Well, if we did that then this would be odd:
> 
>     SELECT to_char(INTERVAL '2 day', 'DD HH24:MI');
>      to_char
>     ----------
>      02 00:00
> 
> or this:
> 
>     SELECT to_char(INTERVAL '2 day 4 hours', 'DD HH24:MI');
>      to_char
>     ----------
>      02 04:00

Mmm. I don't see this is odd...

-- 
Kyotaro Horiguchi
NTT Open Source Software Center

On Fri, Jul 15, 2022 at 04:58:35PM +0900, Kyotaro Horiguchi wrote:
> At Thu, 14 Jul 2022 17:57:32 -0400, Bruce Momjian <bruce@momjian.us> wrote in 
> > On Tue, May 24, 2022 at 01:11:45PM -0700, Nathan Bossart wrote:
> > > The example provided is more like the former (no hour value), because
> > > "timestamp - timestamp" converts 24-hour intervals into days.  In general,
> > > I agree that this probably not a bug.  You probably want to ask to_char()
> > > to display the days as well..
> 
> On the other hand, "interval + interval" doesn't convert hours into
> days. I expected the math to do normalization.
> 
> select INTERVAL '1 day 15hour' + interval '2 day 15 hour';
>     ?column?     
> -----------------
>  3 days 30:00:00
> 
> Is there any means to control over normalization?

Sure, justify_hours():

    SELECT INTERVAL '1 day 15hour' + interval '2 day 15 hour';
        ?column?
    -----------------
     3 days 30:00:00

        SELECT justify_hours(INTERVAL '1 day 15hour' + interval '2 day 15
        hour');
          justify_hours
        -----------------
         4 days 06:00:00

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Indecision is a decision.  Inaction is an action.  Mark Batterson