How to retrieve trips from historical data?

Question

I have the following table mytable in Hive:

id    radar_id     car_id     datetime
1     A21          123        2017-03-08 17:31:19.0
2     A21         


        

Answer 1

select  count(*) / count(distinct to_date(datetime))    as trips_per_day

from   (select  radar_id
               ,datetime
               ,lead(radar_id) over w  as next_radar_id
               ,lead(datetime) over w  as next_datetime                    

        from    mytable

        where   radar_id in ('A21','B15')

        window  w as 
                (
                    partition by  car_id
                    order by      datetime
                )
        ) t

where   radar_id        = 'A21'
    and next_radar_id   = 'B15'
    and datetime + interval '30' minutes >= next_datetime
;

---

+----------------+
| trips_per_day  |
+----------------+
| 1.5            |
+----------------+

P.s.
If your version does not support intervals, the last code record could be replaced by -
and to_unix_timestamp(datetime) + 30*60 > to_unix_timestamp(next_datetime)