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Document Window functions #6338
Description
Is your feature request related to a problem or challenge?
@mustafasrepo and others have contributed to a sophisticated window function implementation in DataFusion like
select x, lag(x, 1) OVER (partition by y, order by x) FROM fooHowever, the user guide does not appear to mention this
Describe the solution you'd like
- Note in the user guide that DataFusion supports window functions
- Add a new page for WindowFunctions (similar to the aggregate function list)
Note the docs (and instructions) are in https://github.com/apache/arrow-datafusion/tree/main/docs
The list of window functions is
- aggregate functions
- The list here https://docs.rs/datafusion-expr/24.0.0/datafusion_expr/window_function/enum.BuiltInWindowFunction.html
Describe alternatives you've considered
No response
Additional context
No response
Reacted by Oleks V
Activity
toppyy commentedon May 20, 2023
started work on this!
toppyy commentedon May 21, 2023
Made a draft PR.
The issue states that the PR should "Note in the user guide that DataFusion supports window functions". Any ideas where exactly to mention this? I had a look and I didn't find a place that felt suitable.
Also, I was on the fence about whether to describe the over-clause with each function as it seems repetative. The alternative would be to described the syntax for window functions on top of the page once in a general form (ie. something like
function(expr) over([partition by expr2] [order by expr3 [ asc | desc ][, …]])). Any thoughts?alamb commentedon May 22, 2023
Thanks @toppyy !
Perhaps we can add a new
Window Functionspage, following the model ofAggregate Functions? (UPDATE: I see this is exactly what you did in #6402 🤦 sorry for not checking that first)I think describing the OVER clause once in general rather than for each function makes much more sense.
Perhaps we can take inspiration (and/or some of the text) from the postgres description: https://www.postgresql.org/docs/current/tutorial-window.html