GROUP BY issue

Hy list.

I have 3 tables:

performance
event
pool_performance

each event has it's performances, and can be assigned to one or more
pools.

pool_performance holds performance_id, pool_id and from_date

performance has event_id and performance_id as primary key

what I want to do is

select min(pool_performance.from_date), pool_id, event_id group by
performance_id

but done in a way that I group only performances belonging to the same
event but for the same pool, and not all performances.

Thanks in advance,

Jure