Hive getting top n records in group by query

Question

I have following table in hive

user-id, user-name, user-address,clicks,impressions,page-id,page-name

I need to find out top 5 users[user-id,user-name,user-ad

Answer 1

Let us say your data looks like following :

page-id   user-id   clicks
page1     user1     10
page1     user2     10
page1     user3     9
page1     user4     8
page1     user5     7
page1     user6     7
page1     user7     6
page1     user8     5
page2     user1     20
page2     user2     19
page2     user3     18

Below Query will give you :

SELECT page-id, user-id, clicks, rank
FROM (
    SELECT page-id, user-id, rank() 
           over (PARTITION BY page-id ORDER BY clicks DESC) as rank, clicks 
    FROM your_table
) ranked_table
WHERE ranked_table.rank <= 5

Result :

page-id   user-id   clicks  rank
page1     user1     10      1
page1     user2     10      1 
page1     user3     9       3 
page1     user4     8       4
page1     user5     7       5 
page1     user6     7       5 
page2     user1     20      1
page2     user2     19      2  
page2     user3     18      3

So, for page1 you are getting 6 users, as users with same number of clicks are ranked same.

But, if you are looking for exactly 5 users, and pick randomly in case multiple users fall in same rank. You can use the below query

SELECT page-id, user-id, clicks, rank
FROM (
    SELECT page-id, user-id, row_number() 
           over (PARTITION BY page-id ORDER BY clicks DESC) as rank, clicks 
    FROM your_table
) ranked_table
WHERE ranked_table.rank <= 5

Result :

page-id   user-id   clicks  rank
page1     user1     10      1
page1     user2     10      2 
page1     user3     9       3 
page1     user4     8       4
page1     user5     7       5 
page2     user1     20      1
page2     user2     19      2  
page2     user3     18      3