I have a table with the fields:

id | group_id
1  | null
2  | null
3  | null
4  | 4
5  | 4
6  | 4
7  | 7
8  | 7
9  | null

and I'd like to sort it to be:

id | group_id
9  | null
7  | 7
8  | 7
4  | 4
5  | 4
6  | 4
3  | null
2  | null
1  | null

So for it to be DESC by id overall, but ASC by id when they share a group_id

Thank you