Help with the IN operator

Question

Hello,
Lets say I have a clients table with ID and client_category
ID CAT
1 1
2 1
3 1
4 2
5 2
6 2
7 3
8 3
9 3
10 3
And I want to select 2 ID's for each client_category.
Desired output:
ID CAT
1 1
2 1
4 2
5 2
7 3
8 3
I'm doing something like:
select cli1.category, (SELECT cli2.client_id FROM xxcli_clienti cli2 WHERE cli1.category=cli2.category and rownum=1) ID
from xxcli_clienti cli1 where cli1.category IN (1,2,3) and rownum<500 order by cli1.category
But with this I get 1 ID for each category.
I tried with GROUP BY and getting only the MAX(client_id), so I run in the same problem.
Thanks in advance

Answer 1

Maybe something like this.
select * from
   select
            <columns> ,
            row_number() over(partition by <grouping_clause> order by <order_clause>) rn
   from
      <table>
where rn <= 2For more information about row_number check this link.
http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/functions001.htm#i81407
Regards
Raj