Обсуждение: Inconsistent Parsing of Offsets with Seconds

Hackers,

The treatment of timestamptz (and timetz) values with offsets that include seconds seems a bit inconsistent. One can
createsuch timestamps through the input function: 

david=# select '2024-06-22T12:35:00+02:30:15'::timestamptz;
      timestamptz
------------------------
 2024-06-22 10:04:45+00

But the offset seconds are dropped (or rounded away?) by to_timestamp()’s `OF` and `TZ` formats[2]:

david=# select to_timestamp('2024-06-03 12:35:00+02:30:15', 'YYYY-MM-DD HH24:MI:SSOF');
      to_timestamp
------------------------
 2024-06-03 10:05:00+00

david=# select to_timestamp('2024-06-03 12:35:00+02:30:15', 'YYYY-MM-DD HH24:MI:SSTZ');
      to_timestamp
------------------------
 2024-06-03 02:05:00-08

The corresponding jsonpath methods don’t like offsets with seconds *at all*:

david=# select jsonb_path_query('"2024-06-03 12:35:00+02:30:15"', '$.datetime("YYYY-MM-DD HH24:MI:SSOF")');
ERROR:  trailing characters remain in input string after datetime format

david=# select jsonb_path_query('"2024-06-03 12:35:00+02:30:15"', '$.timestamp_tz()');
ERROR:  timestamp_tz format is not recognized: "2024-06-03 12:35:00+02:30:15"

I see from the source[1] that offsets between plus or minus 15:59:59 are allowed; should the `OF` and `TZ formats be
ableto parse them? Or perhaps there should be a `TZS` format to complement `TZH` and `TZM`? 

Best,

David

[1] https://github.com/postgres/postgres/blob/70a845c/src/include/datatype/timestamp.h#L136-L142
[2]: https://www.postgresql.org/docs/16/functions-formatting.html

"David E. Wheeler" <david@justatheory.com> writes:
> The treatment of timestamptz (and timetz) values with offsets that include seconds seems a bit inconsistent.

It's hard to get excited about this.  Per the IANA TZ data,
nowhere in the world has used fractional-minute UT offsets
since 1972:

# In 1972 Liberia was the last country to switch from a UT offset
# that was not a multiple of 15 or 20 minutes.

and they were twenty years later than the next-to-last place (although
IANA will steadfastly deny reliability for their TZ data before 1970).
So timestamps like this simply don't exist in the wild.

> The corresponding jsonpath methods don’t like offsets with seconds *at all*:

Perhaps that should be fixed, but it's pretty low-priority IMO.
I doubt there is any standard saying that JSON timestamps need
to be able to include that.

> I see from the source[1] that offsets between plus or minus 15:59:59
> are allowed; should the `OF` and `TZ formats be able to parse them?

I'd vote no.  to_date/to_char already have enough trouble with format
strings being squishier than one might expect.

            regards, tom lane

On Jun 22, 2024, at 13:15, Tom Lane <tgl@sss.pgh.pa.us> wrote:

> It's hard to get excited about this.

I freely admit I’m getting into the weeds here. :-)

>> The corresponding jsonpath methods don’t like offsets with seconds *at all*:
>
> Perhaps that should be fixed, but it's pretty low-priority IMO.
> I doubt there is any standard saying that JSON timestamps need
> to be able to include that.
>
>> I see from the source[1] that offsets between plus or minus 15:59:59
>> are allowed; should the `OF` and `TZ formats be able to parse them?
>
> I'd vote no.  to_date/to_char already have enough trouble with format
> strings being squishier than one might expect.

I believe the former issue is caused by the latter: The jsonpath implementation uses the formatting strings to parse
thetimestamps[1], and since there is no formatting to support offsets with seconds, it doesn’t work at all in JSON
timestampparsing. 

[1]: https://github.com/postgres/postgres/blob/70a845c/src/backend/utils/adt/jsonpath_exec.c#L2420-L2442

So if we were to fix the parsing of offsets in jsonpath, we’d either have to change the parsing code there or augment
theto_timestamp() formats and use them. 

Totally agree not a priority; happy to just pretend offsets with seconds don’t exist in any practical sense.

Best,

David

On Jun 22, 2024, at 14:10, David E. Wheeler <david@justatheory.com> wrote:

> I believe the former issue is caused by the latter: The jsonpath implementation uses the formatting strings to parse
thetimestamps[1], and since there is no formatting to support offsets with seconds, it doesn’t work at all in JSON
timestampparsing. 
>
> [1]: https://github.com/postgres/postgres/blob/70a845c/src/backend/utils/adt/jsonpath_exec.c#L2420-L2442

A side-effect of this implementation of date/time parsing using the to_char templates is that only time zone offsets
andabbreviations are supported. I find the behavior a little surprising TBH: 

david=# select to_timestamp('2024-06-03 12:35:00America/New_York', 'YYYY-MM-DD HH24:MI:SSTZ');
ERROR:  invalid value "America/New_York" for "TZ"
DETAIL:  Time zone abbreviation is not recognized.

Unless the SQL standard only supports offsets and abbreviations, I wonder if we’d be better off updating the above
parsingcode to also try the various date/time input functions, as well as the custom formats that *are* defined by the
standard.

Best,