比如你的事件表是这样的
event(event_id, person_id,....)
那么要查做过所有A事件的人,用不到exists
select persion_id
from event
where event_id = 'A';
要查所有没做过A事件的人,倒可以用not exists(或者用not in)
select distinct person_id
from event x
where not exists (select 'x' from event y
where y.event_id = 'A'
and y.person_id = x.person_id)