On 6/13/21 11:49 AM, Justin Pryzby wrote:
> On Sun, Jun 13, 2021 at 11:25:05AM -0400, Jonathan S. Katz wrote:
>> On 6/13/21 10:57 AM, Zhihong Yu wrote:
>>> +/* Turn multirange into a set of ranges */
>>>
>>> set of ranges: sequence of ranges
>>
>> I believe "set of ranges" is accurate here, as the comparable return is
>> a "SETOF rangetype". Sequences are objects unto themselves.
>>
>
> I believe the point was that (in mathematics) a "set" is unordered, and a
> sequence is ordered. Also, a "setof" tuples in postgres can contain
> duplicates.
The comment in question is part of the header for the
"multirange_unnest" function in the code and AFAICT it is accurate: it
is returning a "set of" ranges as it's literally calling into the
set-returning function framework.
I would suggest leaving it as is.
> The docs say "The ranges are read out in storage order (ascending).", so I
> think this is just a confusion between what "set" means in math vs in postgres.
This is nearly identical to the language in the array unnest[1]
function, which is what I believed Alexander borrowed from:
"Expands an array into a set of rows. The array's elements are read out
in storage order."
If we tweaked the multirange "unnest" function, we could change it to:
+ <para>
+ Expands a multirange into a set of rows.
+ The ranges are read out in storage order (ascending).
+ </para>
to match what the array "unnest" function docs, or
+ <para>
+ Expands a multirange into a set of rows that each
+ contain an individual range.
+ The ranges are read out in storage order (ascending).
+ </para>
to be a bit more specific. However, I think this is also bordering on
overengineering the text, given there has been a lack of feedback on the
"unnest" array function description being confusing.
Thanks,
Jonathan
[1] https://www.postgresql.org/docs/current/functions-array.html