Index on 2 columns

[Tristan Croiset]

I have a table with 2 INT fields (n_id PRIMARY, n_category).

Considering this kind of query :
SELECT n_id, n_category, n_title
FROM news
WHERE n_id <=20035
AND n_category
IN ( 2, 17, 45, 23, 18 )
ORDER BY n_id DESC
LIMIT 1 , 6

What's the best Index I should use ?

I firstly thought to create a index on 2 columns (n_id then n_category) but I wonder if it will be really usefull and if the best index for this query is just the primary on n_id.

Thanks