an difficult SQL

Hi Everybody,

I was wondering if anybody here could help me cook up a query:

1. against a list of events (like an activity log in the database). The
list is a single table: create table events (tm timestamp, user int,
description text).

2. of which the output would be sorted in such a way, that:
2.1 most recent event would "select" most recent events of that same
user, and displayed in a group (of say 10) of them (in "tm" order).

2.2 going through the events back in time, first event of ANOTHER user
selects next group, where (say 10) most recent events of that OTHER user
is presented.

2.3 next most recent event of yet another user selects yet another group
to display and this selection process goes on, up to a maximum of (say
20) users/groups-of-their-events.

2.4 after that, all other events are selected in tm order.

This is to present most recent telephone activities grouped by most
recent subscribers so that the dashboard doesn't get cluttered with
information but allows for an overview of other activity of most recent
users.

I tend to think, that it's a problem for a window function ... but I've
stumbled on the problem how to limit the window "frame" to just a few
(say 10) events within the "window" and have all the rest returned as
"tail" of the query.

BTW: the eventlog table is big. (and partitioned).

Any help appreciated.

-R