Group by an individual timeframe - sql

Question

I would like to group rows of a table by an individual time frame.
As an example let's imagine we have a list of departures at an airport:
| Departure | Flight | Destination |
| 2016-06-01 10:12:00 | LH1234 | New York |
| 2016-06-02 14:23:00 | LH1235 | Berlin |
| 2016-06-02 14:30:00 | LH1236 | Tokio |
| 2016-06-03 18:45:00 | LH1237 | Belgrad |
| 2016-06-04 04:10:00 | LH1237 | Rio |
| 2016-06-04 06:20:00 | LH1237 | Paris |
I can easily group the data by full hours (days, weeks, ...) using the following query:
select to_char(departure, 'HH24') as "full hour", count(*) as "number flights"
from departures
group by to_char(departure, 'HH24')
This should result in the following table.
| full hour | number flights |
| 04 | 1 |
| 06 | 1 |
| 10 | 1 |
| 14 | 2 |
| 18 | 1 |
Now my question: Is there an elegant way (or best practise) to group data by an individual time frame.
The result I'm looking for is the following:
| time frame | number flights |
| 2016-05-31 22:00 - 2016-06-01 06:00 | 0 |
| 2016-06-01 06:00 - 2016-06-01 14:00 | 1 |
| 2016-06-01 14:00 - 2016-06-01 22:00 | 0 |
| 2016-06-01 22:00 - 2016-06-02 06:00 | 0 |
| 2016-06-02 06:00 - 2016-06-02 14:00 | 0 |
| 2016-06-02 14:00 - 2016-06-02 22:00 | 2 |
| 2016-06-02 22:00 - 2016-06-03 06:00 | 0 |
| 2016-06-03 06:00 - 2016-06-03 14:00 | 0 |
| 2016-06-03 14:00 - 2016-06-03 22:00 | 1 |
| 2016-06-03 22:00 - 2016-06-04 06:00 | 1 |
| 2016-06-04 06:00 - 2016-06-04 14:00 | 1 |
| 2016-06-04 14:00 - 2016-06-04 22:00 | 0 |
| 2016-06-04 22:00 - 2016-06-05 06:00 | 0 |
(The rows with 0 flights aren't relevant. They are just there for a better visualization of the problem.)
Thanks for your answers in advance. :-)
Peter

Answer 1

Since you have groups starting at 22:00 and multiples of 8 hours afterwards then you can use TRUNC() and an offset of 2 hours to get the results grouped by each day.
You can then work out the which third of the day the departure is in and also group by that:
GROUP BY TRUNC( Departure + 2/24 ),
FLOOR( ( Departure + 2/24 - TRUNC( Departure + 2/24 ) ) * 3 )

Answer 2

Something like this should work. Please note the two input variables, first_time and timespan. The timespan is whatever you want it to be (I wrote it in the form 8/24 for eight hours; if you make timespan into a bind variable as a number expressed in HOURS, you need the division by 24). Due to the way I wrote the formulas, there are NO requirements on first_time other than it should be one of your boundary date/times; it may even be in the future, it won't change the results. It may also be made into a bind variable, then you can decide in what format you want it to be made available to the query.
with timetable (departure, flight, destination) as (
select to_date('2016-06-01 10:12:00', 'yyyy-mm-dd hh24:mi:ss'), 'LH1234', 'New York'
from dual union all
select to_date('2016-06-02 14:23:00', 'yyyy-mm-dd hh24:mi:ss'), 'LH1235', 'Berlin'
from dual union all
select to_date('2016-06-02 14:30:00', 'yyyy-mm-dd hh24:mi:ss'), 'LH1236', 'Tokyo'
from dual union all
select to_date('2016-06-03 18:45:00', 'yyyy-mm-dd hh24:mi:ss'), 'LH1237', 'Belgrad'
from dual union all
select to_date('2016-06-04 04:10:00', 'yyyy-mm-dd hh24:mi:ss'), 'LH1237', 'Rio'
from dual union all
select to_date('2016-06-04 06:20:00', 'yyyy-mm-dd hh24:mi:ss'), 'LH1237', 'Paris'
from dual
),
input_values (first_time, timespan) as (
select to_date('2010-01-01 06:00:00', 'yyyy-mm-dd hh24:mi:ss'), 8/24 from dual
),
prep (adj_departure, flight, destination) as (
select first_time + timespan * floor((departure - first_time) / timespan),
flight, destination
from timetable, input_values
)
select to_char(adj_departure, 'yyyy-mm-dd hh24:mi:ss') || ' - ' ||
to_char(adj_departure + timespan, 'yyyy-mm-dd hh24:mi:ss') as time_interval,
count(*) as ct
from prep, input_values
group by adj_departure, timespan
order by adj_departure
;
Output:
TIME_INTERVAL CT
----------------------------------------- ----------
2016-06-01 06:00:00 - 2016-06-01 14:00:00 1
2016-06-02 14:00:00 - 2016-06-02 22:00:00 2
2016-06-03 14:00:00 - 2016-06-03 22:00:00 1
2016-06-03 22:00:00 - 2016-06-04 06:00:00 1
2016-06-04 06:00:00 - 2016-06-04 14:00:00 1