How to use self-join to get records within the last n days in SQL?


This Content is from Stack Overflow. Question asked by titutubs

I have a table with users that come to purchase products on some dates. Now I want to create a query where I see for each user, what their purchase data was within the last 14 days from a given date. Is self-join the best option for such operation? I tried:

Select a.user_id,, avg(b.sales) avg_sales
from purchase a
join purchase b
on a.user_id=b.user_id
and>dateadd('day',-14, --get data for last 14 days from (i.e. if is 2020-01-16, then get the avg of all purchases from 2020-01-01 TO 2020-01-15)

This query is not working as expected and takes also too long.


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