From: Andreas Bergmaier <ab@principiamentis.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-docs@lists.postgresql.org <pgsql-docs@lists.postgresql.org>
Cc: pgsql-bugs@lists.postgresql.org <pgsql-bugs@lists.postgresql.org>
Subject: Re: BUG #16022: to_json on arrays with unusual lower bound is not intuitive
Date: Thu, 26 Sep 2019 13:09:03 +0000
Message-ID: <f5446e31-4e39-3c90-7bf9-3805fe9f282c@principiamentis.com> (raw)
In-Reply-To: <23022.1569422056@sss.pgh.pa.us>
References: <16022-5c864f8a572d5b5b@postgresql.org>
<23022.1569422056@sss.pgh.pa.us>
Hi!
On 25.09.19 16:34, Tom Lane wrote:
> PG Bug reporting form <noreply@postgresql.org> writes:
>> I would expect the array indices of a JSON array to match with the
>> subscripts of a postgres array when converting them back and forth.
>> However, Postgres lets the JSON array begin at the `lower_bound` of the
>> array, not at subscript 1 (= index 0).
>> For example, `to_json('[-2:5]={-2,-1,0,1,2,3,4,5}'::int[])` results in
>> `[-2,-1,0,1,2,3,4,5]` where I would have expected `[1,2,3,4,5]` (or an
>> error, since JSON arrays must not have negative indices).
>
> I can see no reason whatever for either of those definitions to be
> better than the established one. If you want some other conversion
> rule, write your own function that behaves the way you want.
OK, I agree it's kinda unreasonable to change this.
However, I would like to see this behaviour documented at
https://www.postgresql.org/docs/current/functions-json.html, so FUP'd to
pgsql-docs.
I propose to add the following description to Table 9.45:
| The resulting JSON array starts at the lower bound of the PostgreSQL
array, regardless whether that is 1 or not.
Maybe also add `to_json('[3:8]={3,4,5,6,7,8}'::int[])` becoming
`[3,4,5,6,7,8]` to the examples.
While we're at it, I would also like to see the documentation of
`array_lower` and `array_upper` to be improved in
https://www.postgresql.org/docs/current/functions-array.html. I was a
bit surprised that when passing an empty array, they did return `NULL`
instead of the "default" value `1`. Can you add that as an example to
the two table rows, or just add a simple "(NULL if empty)" parenthetical
to their descriptions?
Alternatively, document it after the table:
| In `array_lower` and `array_upper`, `NULL` is returned if the array
dimension does not exist or is empty.
kind regards,
Andreas Bergmaier
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Subject: Re: BUG #16022: to_json on arrays with unusual lower bound is not intuitive
In-Reply-To: <f5446e31-4e39-3c90-7bf9-3805fe9f282c@principiamentis.com>
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