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
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