使用cte在最后生成会话组和聚合：

with recursive cte(user_name, id, dt, c_id) as (
    select e.user_name, min(e.id), min(e.event_datetime), min(e.id) from events e 
    group by e.user_name
    union all
    select c.user_name, e.id, e.event_datetime, case when extract(epoch from e.event_datetime - c.dt) > 600 then e.id else c.c_id end 
    from cte c join events e on e.user_name = c.user_name and 
        e.event_datetime = (select min(e1.event_datetime) from events e1 where e1.user_name = c.user_name and e1.event_datetime > c.dt)
),
session_events as (
    select c.user_name, c.c_id, e.event_name, count(*) e_c from cte c join events e on e.event_datetime = c.dt group by c.user_name, c.c_id, e.event_name
)
-- average session duration for certain users (specified in parenthesis)
select avg(t1.av) av_session_sec 
from (select t.user_name, avg(extract(epoch from t.m2 - t.m1)) av 
      from (select c.user_name, c.c_id, min(c.dt) m1, max(c.dt) m2 
            from cte c group by c.user_name, c.c_id) t 
      where t.user_name in ('Jack', 'Ashley', 'Bob')
      group by t.user_name) t1
-- average number of sessions
select avg(t.s_c) av_sessions from (select c.user_name, count(distinct c.c_id) s_c 
   from cte c group by c.user_name) t
-- Most common activity per session per group
select t.*, e1.event_name from (select e.user_name, e.c_id, max(e.e_c) m from session_events e group by e.user_name, e.c_id) t
join session_events e1 on e1.user_name = t.user_name and e1.e_c = t.m
where t.user_name in ('Jack', 'Ashley')

See fiddle