Function to get rolling average with lowest 2 values eliminated? - sql

Question

This is my sample data with the current_Rating column my desired output.
Date Name Subject Importance Location Time Rating Current_rating
12/08/2020 David Work 1 London - - 4
1/08/2020 David Work 3 London 23.50 4 3.66
2/10/2019 David Emails 3 New York 18.20 3 4.33
2/08/2019 David Emails 3 Paris 18.58 4 4
11/07/2019 David Work 1 London - 3 4
1/06/2019 David Work 3 London 23.50 4 4
2/04/2019 David Emails 3 New York 18.20 3 5
2/03/2019 David Emails 3 Paris 18.58 5 -
12/08/2020 George Updates 2 New York - - 2
1/08/2019 George New Appointments5 London 55.10 2 -
I need to use a function to get values in the current_Rating column.The current_Rating gets the previous 5 results from the rating column for each name, then eliminates the lowest 2 results, then gets the average for the remaining 3. Also some names may not have 5 results, so I will just need to get the average of the results if 3 or below, if 4 results I will need to eliminate the lowest value and average the remaining 3. Also to get the right 5 previous results it will need to be sorted by date. Is this possible? Thanks for your time in advance.

Answer 1

What a pain! I think the simplest method might be to use arrays and then unnest() and aggregate:
select t.*, r.current_rating
from (select t.*,
array_agg(rating) over (partition by name order by date rows between 4 preceding and current row) as rating_5
from t
) t cross join lateral
(select avg(r) as current_rating
from (select u.*
from unnest(t.rating_5) with ordinality u(r, n)
where r is not null
order by r desc desc
limit 3
) r
) r