Slow join on large tables

[Mark Smith]

Hello:

I have two tables:
D (500,000 recs), and DL (2,500,000 recs)

D has a PK and an index on HLQ. DL has a PK and an index on ID.

The following SQL:
SELECT
HLQ as "HLQ",
count(*)
FROM
D, DL
WHERE
D.DLID=DL.ID
GROUP BY HLQ

produces the following explain:
table type possible_keys key key_len ref rows Extra
D ALL 500000 Using where; Using temporary; Using filesort

DL eq_ref ID ID 4 D.DLID 1 Using index

The query takes ~ 3:30 on a Athlon xp2200; 1GB RAM; default bufer
settings.
Adding the following buffer settings only slightly decrerased the time
(~3:00).
key_buffer=512M
table_cache=256
sort_buffer=16M
read_buffer_size=16M

It appeasrs that the 'Using filesort' on table D is due to the Group
By clause and is the problem. I have an index on HLQ. Is there any
way to get MySQL to use it?

Any other suggestions would be appreciated.

Thanks
Mark