Re: Overlapping timestamptz ranges with priority

On 7/3/21 9:32 AM, Ray O'Donnell wrote:
> On 27/06/2021 23:41, Ray O'Donnell wrote:
>> Hi all,
>>
>> I'm playing with timestamptz ranges for a hobby project. I have a
>> table with a tstzrange column, in which the timestamps can overlap;
>> where they do, rows with a higher priority (derived from a bigint
>> primary key column) should be picked.
>>
>> What I'd like to do is present a view which shows timestamp ranges at
>>  the front of the queue, as it were; where ranges overlap, these may
>> be segments of a range from a particular row. I'm having trouble with
>> this and would appreciate suggestions.
>
> I've come up with a way of doing it using a function... it's not going
> to be very efficient if the number of rows gets large, due to nested
> loops, but as the system generally keeps only a limited number of
> bookings (no more that a few hundred), I think it'll do - certainly as a
> first run at it.
>
> Firstly, the table structure (as it now stands) on which the function
> will operate:
>
> CREATE TABLE bookings
> (
>     booking_id bigint NOT NULL GENERATED ALWAYS AS IDENTITY,
>     aircraft_reg text NOT NULL,
>     type_code text NOT NULL,
>     booking_time tstzrange NOT NULL,
>     owner_uid text NOT NULL,
>     owner_name text NOT NULL,
>
>     CONSTRAINT bookings_pk PRIMARY KEY (booking_id),
>
>     (... foregin keys etc...)
> );
>
>
> And here's the function:
>
> create or replace function get_visible_bookings()
> returns setof bookings
> language plpgsql
> as
> $$
> declare
>   m_rec bookings;
>   m_overlapping record;
>   m_visible_time tstzrange;
> begin
>   -- Loop through all bookings on the system, ordered on booking ID.
>   -- The booking ID also give the queue priority of the booking:
>   -- bookings with a lower ID have a higher priority.
>   for m_rec in
>     select * from bookings order by booking_id
>   loop
>     m_visible_time := m_rec.booking_time;
>
>     -- For each booking, check whether there are any with
>     -- a higher priority and whose times overlap it.
>     for m_overlapping in
>       select booking_id, booking_time from bookings
>       where booking_id < m_rec.booking_id
>       and booking_time && m_rec.booking_time
>     loop
>       -- Snip away any overlapping (obscured) time.
>       m_visible_time := m_visible_time - m_overlapping.booking_time;
>     end loop;
>
>     -- If any of the current booking's time is still visible,
>     -- then return the row with what's left of the time.
>     if not isempty(m_visible_time) then
>     return next row(m_rec.booking_id, m_rec.aircraft_reg,
>           m_rec.type_code, m_visible_time,
>           m_rec.owner_uid, m_rec.owner_name);
>     end if;
>   end loop;
>
>   return;
> end;
> $$;

I'm not sure this is doing what you think it is;

select * from bookings order by booking_id;
booking_id | aircraft_reg | type_code |
booking_time | owner_uid | owner_name
------------+--------------+-----------+-----------------------------------------------------+-----------+-----
1 | A1ZX | type1 | ["2021-07-03
10:00:00-07","2021-07-03 14:00:00-07"] | 1 | aklaver
2 | A1ZX | type1 | ["2021-07-03
12:00:00-07","2021-07-03 16:00:00-07"] | 1 | aklaver
3 | A1ZX | type1 | ["2021-07-04
09:00:00-07","2021-07-04 12:00:00-07"] | 1 | aklaver
4 | B2CA | type2 | ["2021-07-03
09:00:00-07","2021-07-03 12:00:00-07"] | 2 | wilbur
5 | B2CA | type2 | ["2021-07-03
11:00:00-07","2021-07-03 14:00:00-07"] | 2 | wilbur

select * from get_visible_bookings();
booking_id | aircraft_reg | type_code |
booking_time | owner_uid | owner_name
------------+--------------+-----------+-----------------------------------------------------+-----------+------------
1 | A1ZX | type1 | ["2021-07-03
10:00:00-07","2021-07-03 14:00:00-07"] | 1 | aklaver
2 | A1ZX | type1 | ("2021-07-03
14:00:00-07","2021-07-03 16:00:00-07"] | 1 | aklaver
3 | A1ZX | type1 | ["2021-07-04
09:00:00-07","2021-07-04 12:00:00-07"] | 1 | aklaver
4 | B2CA | type2 | ["2021-07-03
09:00:00-07","2021-07-03 10:00:00-07") | 2 | wilbur
(4 rows)

The booking_id for aircraft B2CA with booking_time of ["2021-07-03
11:00:00-07","2021-07-03 14:00:00-07"] is not accounted for. There is a
step missing that accounts for bookings being assigned to a particular
aircraft.

>
>
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com