table events {
        id    primary key,
        name  varchar
    }

    table sessions {
        id       primary key,
        event    references events(id),
        starts   datetime
    }

##</code><code>##

    select  e.name, s.starts
      from  events e
      join  sessions s on e.id = s.event
      join  ( select  event, min(starts) as starts
                from  sessions
               group  by event
            ) as t
        on  s.event = t.event
       and  s.time  = t.starts