这是一种群岛问题。我将建议一个累积最大值方法来确定这些岛屿的起点。这样做的目的是确定岛屿，然后总结其价值：

select user_id, episode_name, min(start_time), max(end_time)
from (select t.*,
             sum(case when prev_end_time >= start_time then 0 else 1 end) over
                 (partition by user_id, episode_name order by start_time) as grp
      from (select t.*,
                   max(end_time) over (partition by user_id, episode_name
                                       order by start_time
                                       rows between unbounded preceding and 1 preceding
                                      ) as prev_end_time
            from t
           ) t
     ) t
group by user_id, episode_name, grp;

要获得总数，可以使用附加的聚合级别：

with cte as (
      select user_id, episode_name, min(start_time) as start_time, max(end_time) as end_time
      from (select t.*,
                   sum(case when prev_end_time >= start_time then 0 else 1 end) over
                       (partition by user_id, episode_name order by start_time) as grp
            from (select t.*,
                         max(end_time) over (partition by user_id, episode_name
                                             order by start_time
                                             rows between unbounded preceding and 1 preceding
                                            ) as prev_end_time
                  from t
                 ) t
           ) t
      group by user_id, episode_name, grp
     )
select user_id, episode_name, sum(end_time - start_time)
from cte
group by user_id, episode_name;