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* Suggestion for docs, section "4.2.3 Subscripts": bounds and base
@ 2025-04-03 18:22 PG Doc comments form <noreply@postgresql.org>
2025-04-07 08:03 ` Re: Suggestion for docs, section "4.2.3 Subscripts": bounds and base Laurenz Albe <laurenz.albe@cybertec.at>
2025-04-07 13:51 ` Re: Suggestion for docs, section "4.2.3 Subscripts": bounds and base David G. Johnston <david.g.johnston@gmail.com>
0 siblings, 2 replies; 3+ messages in thread
From: PG Doc comments form @ 2025-04-03 18:22 UTC (permalink / raw)
To: pgsql-docs@lists.postgresql.org; +Cc: s@xss.de
The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/17/sql-expressions.html
Description:
I skimmed over section 4.2 while waiting for a meeting to start and found no
mention of the following two questions that immediately pop up in my mind
when subscripts are mentionned:
Are subscripts 0-based or 1-based?
Are slice boundaries inclusive or exclusive?
Suggestion:
...
`expression[subscript]`
where by default the subscript is counted from 1. A contiguous slice of
array elements can be extracted by using the subscript of the first and last
element to be included in the slice:
`expression[first_included_subscript:last_included_subscript]`
Regards,
s.
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Suggestion for docs, section "4.2.3 Subscripts": bounds and base
2025-04-03 18:22 Suggestion for docs, section "4.2.3 Subscripts": bounds and base PG Doc comments form <noreply@postgresql.org>
@ 2025-04-07 08:03 ` Laurenz Albe <laurenz.albe@cybertec.at>
1 sibling, 0 replies; 3+ messages in thread
From: Laurenz Albe @ 2025-04-07 08:03 UTC (permalink / raw)
To: s@xss.de; pgsql-docs@lists.postgresql.org
On Thu, 2025-04-03 at 18:22 +0000, PG Doc comments form wrote:
> Page: https://www.postgresql.org/docs/17/sql-expressions.html
> Description:
>
> I skimmed over section 4.2 while waiting for a meeting to start and found no
> mention of the following two questions that immediately pop up in my mind
> when subscripts are mentionned:
>
> Are subscripts 0-based or 1-based?
This question is answered in the documentation of the array data types:
https://www.postgresql.org/docs/current/arrays.html
The array subscript numbers are written within square brackets. By default
PostgreSQL uses a one-based numbering convention for arrays, that is, an
array of n elements starts with array[1] and ends with array[n].
> Are slice boundaries inclusive or exclusive?
That becomes clear on the same page:
We can also access arbitrary rectangular slices of an array, or subarrays.
An array slice is denoted by writing lower-bound:upper-bound for one or
more array dimensions. For example, this query retrieves the first item
on Bill's schedule for the first two days of the week:
SELECT schedule[1:2][1:1] FROM sal_emp WHERE name = 'Bill';
schedule
------------------------
{{meeting},{training}}
(1 row)
Admittedly, there is no exact definition, but the example makes clear that
the boundaries are inclusive.
I don't think that we need to repeat that information.
Yours,
Laurenz Albe
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Suggestion for docs, section "4.2.3 Subscripts": bounds and base
2025-04-03 18:22 Suggestion for docs, section "4.2.3 Subscripts": bounds and base PG Doc comments form <noreply@postgresql.org>
@ 2025-04-07 13:51 ` David G. Johnston <david.g.johnston@gmail.com>
1 sibling, 0 replies; 3+ messages in thread
From: David G. Johnston @ 2025-04-07 13:51 UTC (permalink / raw)
To: s@xss.de <s@xss.de>; pgsql-docs@lists.postgresql.org <pgsql-docs@lists.postgresql.org>
On Thursday, April 3, 2025, PG Doc comments form <noreply@postgresql.org>
wrote:
> The following documentation comment has been logged on the website:
>
> Page: https://www.postgresql.org/docs/17/sql-expressions.html
> Description:
>
> I skimmed over section 4.2 while waiting for a meeting to start and found
> no
> mention of the following two questions that immediately pop up in my mind
> when subscripts are mentionned:
>
> Are subscripts 0-based or 1-based?
> Are slice boundaries inclusive or exclusive?
>
The answers depend on the data type to which the [ ] operation is being
applied. And we haven’t really covered data type at this point. So
probably we should just acknowledge these nuances exist and say you can
find the answers for a given data type in its reference page. As a reader,
then, it is registered as an unimportant detail within the overall learning
of the grammar. (I’ll have a more precise answer when I have a moment to
re-read these docs.)
David J.
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2025-04-03 18:22 Suggestion for docs, section "4.2.3 Subscripts": bounds and base PG Doc comments form <noreply@postgresql.org>
2025-04-07 08:03 ` Laurenz Albe <laurenz.albe@cybertec.at>
2025-04-07 13:51 ` David G. Johnston <david.g.johnston@gmail.com>
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