Обсуждение: Possibly misleading documentation of Template Patterns for Date/Time Formatting

David Kubecka <davidkubecka366@gmail.com> writes:
> on the official docs
> https://www.postgresql.org/docs/9.6/functions-formatting.html see the table
> 9-24 and Pattern "Q". The doc (for version 9.6) says:

> quarter (ignored by to_date and to_timestamp)

> All the later versions of the doc (10, 11, 12) miss the "ignored" note

It's still there, just further down:

  * In to_timestamp and to_date, weekday names or numbers (DAY, D, and
    related field types) are accepted but are ignored for purposes of
    computing the result. The same is true for quarter (Q) fields.

I think this was changed because we noticed that the docs failed to point
out the issue for weekday fields, and cramming similar annotations into
their already-long table entries didn't make sense.  So the info got moved
to the commentary below.

            regards, tom lane

Hi,

on the official docs https://www.postgresql.org/docs/9.6/functions-formatting.html see the table 9-24 and Pattern "Q". The doc (for version 9.6) says:

quarter (ignored by to_date and to_timestamp)

All the later versions of the doc (10, 11, 12) miss the "ignored" note leading the user to think that it should work but it doesn't, at least on 12.1:

# select TO_DATE( '2012-4', 'YYYY-Q' );
  to_date  
------------
 2012-01-01
(1 row)

Is this an expected behaviour, i.e. the documentation is just wrong or it really should work?

David Kubecka <davidkubecka366@gmail.com> writes:
> Anyway, could you shed some light if there's any particular reason why TO_DATE(
> '2012-4', 'YYYY-Q' ) isn't supported?

You can't compute a specific date from that.  Nor does it lend itself to
combination with other fields to reach a specific date --- adding DD
doesn't do it, and if you add MM, you might as well not bother with Q.

            regards, tom lane