Matched size random samples from hive table

Question

I have a hive table activity with columns userid, itemid, and rating, with possible ratings of 1 and 0, in which there ar

Answer 1

If there are a lot of classes, you can use the following query to get samples across all the classes without writing the query multiple times:

select * from 
    (select userid, item_id, rating, 
    row_number() over(partition by rating  order by rand()) as rn 
    from activity
    ) a 
where rn <= x

x can be whatever the count you want each class to be of.