SQL Lead & Lag to find gap between dates

Question

i have a table with two columns event_start and event_end :
CREATE TABLE MYBATCHTAB
  EVENT_START  DATE                             NOT NULL,
  EVENT_END    DATE                             NOT NULL
and my data is :
Insert into MYBATCHTAB
   (EVENT_START, EVENT_END)
Values
   (TO_DATE('08/12/2013 22:45:00', 'MM/DD/YYYY HH24:MI:SS'), TO_DATE('08/12/2013 23:55:00', 'MM/DD/YYYY HH24:MI:SS'));
Insert into MYBATCHTAB
   (EVENT_START, EVENT_END)
Values
   (TO_DATE('08/12/2013 15:30:00', 'MM/DD/YYYY HH24:MI:SS'), TO_DATE('08/12/2013 17:00:00', 'MM/DD/YYYY HH24:MI:SS'));
Insert into MYBATCHTAB
   (EVENT_START, EVENT_END)
Values
   (TO_DATE('08/12/2013 16:00:00', 'MM/DD/YYYY HH24:MI:SS'), TO_DATE('08/12/2013 17:30:00', 'MM/DD/YYYY HH24:MI:SS'));
Insert into MYBATCHTAB
   (EVENT_START, EVENT_END)
Values
   (TO_DATE('08/12/2013 20:00:00', 'MM/DD/YYYY HH24:MI:SS'), TO_DATE('08/12/2013 22:00:00', 'MM/DD/YYYY HH24:MI:SS'));
COMMIT;
Event Start
Event End
08/12/2013 15:30:00
08/12/2013 17:00:00
08/12/2013 16:00:00
08/12/2013 17:30:00
08/12/2013 20:00:00'
08/12/2013 22:00:00
08/12/2013 22:45:00
08/12/2013 23:55:00
and i want to find the first whole start - end period in this example start : 15:30 - end 17:30 (merging  record 1&2 )
but not the third one for example not 15.30 - 22:00 or not 15.30 23:55 because there are gaps between end dates.
how can i do this using lead&lag ? 
I'm not sure if this is the best approach

Answer 1

Maybe a baby-step solution
select event_start,event_end
  from (select event_start,
               case when overlap is not null
                    then case when lead(overlap,1) over (order by event_start) is not null
                              then lead(event_end,1) over (order by event_start)
                              when lag(overlap,1) over (order by event_start) is not null
                              then null
                         end
                    else event_end
               end event_end
          from (select event_start,event_end,
                       case when lead(event_start,1) over (order by event_start) <= event_end
                              or lag(event_end,1) over (order by event_start) >= event_start
                            then 'overlap'
                       end overlap
                  from mybatchtab
where event_end is not null
order by event_start
EVENT_START
EVENT_END
08/12/2013 15:30:00
08/12/2013 17:30:00
08/12/2013 20:00:00
08/12/2013 22:00:00
08/12/2013 22:45:00
08/12/2013 23:55:00
or when there can be more than two consecutive overlaps
select event_start,
       event_end
  from (select case when lag_overlap is null
                    then event_start
               end event_start,
               case when coalesce(lead_overlap,lag_overlap) is null
                    then event_end
                    when lag_overlap is null and lead_overlap is not null
                    then lead(event_end) over (order by event_start)
                end event_end
          from (select event_start,event_end,
                       case when event_start < lag(event_end) over (order by event_start)
                            then 'overlap'
                       end lag_overlap,
                       case when event_end > lead(event_start) over (order by event_start)
                            then 'overlap'
                       end lead_overlap
                  from mybatchtab
         where lead_overlap is null
            or lag_overlap is null
where event_end is not null
   and event_end is not null
order by event_start
Regards
Etbin