Question

I need to limit the results from a query, but I can’t implement any example I’ve seen using count and rownum. Given this table

rec error
___ _____
  1   123
  2   123
  3   456
  4   456
  5   456
  6   456
  7   456
  8   456
  9   456
 10   789
 11   789
 12   789
 13   789

This table has many more rows with many different error codes. I’m using this to get the records i need:

select rec, error from table where error in (123,456,789)

But say I want to only return no more than 2 records per error. I’m not sure how to do this. If I was only looking for a single error, I could simply use count or rownum. Not sure how to do it when using the IN condition.

Answer 1

Do you care which two rows you get for any particular error code? Something like this will get you the two rows for each error code with the smallest rec value. If you change the ORDER BY in the ROW_NUMBER analytic function, you can change which two rows are returned.

SELECT rec,
       error
  FROM (SELECT rec,
               error,
               row_number() over (partition by error
                                      order by rec asc) rnk
          FROM your_table_name)
 WHERE error in (123,456,789)
   AND rnk <= 2