Você pode tentar isso :)
SELECT *, (SELECT COUNT(*)+1
FROM [sometbl] counter
WHERE t.groups = counter.groups
AND t.description > counter.description) AS Counter
FROM [sometbl] t
DEMO
SELECT *, (SELECT COUNT(*)+1
FROM [sometbl] counter
WHERE t.groups = counter.groups
AND t.description > counter.description) AS Counter
FROM [sometbl] t