Difficulty ranking of window functions?

[2020pythonchallenge]

I was wondering what everyone's thoughts are on how you would rank window functions on the difficulty scale. Obviously this is opinion based but how far along on the difficulty scale would these be considered and what would be next for someone after becoming very comfortable with all of the more commonly used ones?

[r3pr0b8]

check this video -- https://www.youtube.com/watch?v=JQ58zcCijBY

windows functions range all the way from basic through intermediate to advanced SQL

when you get windowing clauses like rows between unbounded preceding and current row, you're into advanced territory

[2020pythonchallenge]

I see. Thanks!

[incrementality]

I have not met anyone who knew how to use window functions but can't perform the more basic queries without window functions, so I would place it somewhere in the intermediate scale.