Re: Window function docs

On Thu, Apr 6, 2017 at 2:49 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:

> As part of writing a talk about window functions, I have done some
> cleanups of the window function docs, attached, that I would like to
> apply to head.

+1 Overall. Some minor technical items noted below. The only conceptual
item is whether (and, if so, how) to deal with partitions vs. frames.

​- But unlike regular aggregate functions, use of a window function does
not
+ But unlike normal aggregate functions, use of a window function does
not

How broadly did you look for usage of normal versus regular? The window
function doc page uses "normal" once, vis-a-vis "ordered-set", I haven't
looked further. Note on that page the intro paragraph doesn't mention
hypothetical-set aggregates as being distinct from ordered-set aggregates
yet the tables and the docs here do.

https://www.postgresql.org/docs/current/static/functions-aggregate.html

+ treated as a window function and computed across the entire partition.)

Would introducing the concept of frame here trade precision for
comprehension?

- <firstterm>window frame</>. Many (but not all) window functions act
only
+ <firstterm>window frame</>. Some window functions act only

This is a semantic change as to whether the dominate behavior is to act on
frames or partitions. IIUC very few window functions, when presented with
a ORDER BY'd OVER and thus a limited frame, will still act on the entire
partition instead of the just the frame they are provided. In particular
don't all normal aggregates (and user-defined ones) operate on frames? The
cume_dist function noted later is one of the few exceptions since it
effectively operates on both - the frame for the numerator and the
partition for the denominator.

+ aggregate function (i.e. not ordered-set or hypothetical-set aggregates)

I, and others, subscribe to the believe that both i.e., and e.g., should
have trailing commas...

http://english.stackexchange.com/questions/6894/should-there-be-a-comma-after-i-e

+ functions (includes <function>cume_dist</>) are defined so that they

s/b "including <function>cume_dist</>"

+ give the same answer for any two peer rows.

for all peer rows?

+ assuming the current row is does not exist in the partition.

remove "is"