Help with Covering Index

[Erin ONeill]

Data warehousing is not my specialty I need a covering index on a stats query and I'm just not getting it.

I have 3 main queries.

Here's one
explain SELECT DISTINCT l.show_id,l.episode_id,l.hitday,SUM(traffic)/1048576 AS traffic, COUNT(longip) AS hit_count,COUNT(distinct longip) AS unique_hit_count
FROM o_hits AS l
WHERE l.status BETWEEN 100 AND 199
GROUP BY l.show_id,l.episode_id,l.hitday


I've tired:
index on status
index on status,show_id,episode_id, hitday

Explain will say something like this:
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: l
type: ALL
possible_keys: cover
key: NULL
key_len: NULL
ref: NULL
rows: 22329227
Extra: Using where; Using filesort

I'm just missing it. I know I'm staring at the answer but can't seem to see it.

Thoughts? suggestions?

Thanks
erin