Re: Help with writing a generate_series(tsmultirange, interval)

Hello Adrian,

> Le 31 juill. 2021 à 15:49, Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com> a écrit :
>
> On 7/31/21 11:59 AM, François Beausoleil wrote:
>> Hello all!
>> I’m excited for multi ranges, as they fit nicely into a scheduling app. What I’m trying to express is something along the lines of « Every weekday from 2021-08-01 and 2021-10-01, from 9 AM to 8 PM, every 90 minutes ». You can think of public transit for the model.
>> Initially, I was going to create a table with every departure recorded, and was going to refresh the table on every write to the parent table, but that means maintaining many rows for every change to the schedule. Then, I remembered multi ranges in PG14, and they fit nicely with what I had in mind.
>> Now that I can store the info I want, I’d like to iterate over the ranges, so I can generate the exact departure times, something similar to this:
>> SELECT instant
>> FROM generate_series(
>> '{["2021-08-02 08:00:00","2021-08-02 11:00:00"),["2021-08-03 08:00:00","2021-08-03 20:00:00"]’}
>> , interval ’90 minutes’) as instant;
>> 2021-08-02 08:00
>> 2021-08-02 09:30
>> — 2021-08-02 11:00 excluded as the range excludes its upper bound
>> 2021-08-03 08:00:00
>> 2021-08-03 09:30:00
>> 2021-08-03 11:00:00
>> 2021-08-03 12:30:00
>> 2021-08-03 14:00:00
>> 2021-08-03 15:30:00
>> 2021-08-03 17:00:00
>> 2021-08-03 18:30:00
>> 2021-08-03 20:00:00 — included, as the upper bound is inclusive
>> That function doesn’t exist, and I can’t seem to find a function to iterate over a multi range either. Does such a function exist? I’m specifically looking at https://www.postgresql.org/docs/14/functions-range.html.
>> This is a toy application, a spike to see what’s possible.
>> I wanted to avoid maintaining a table with hundreds of rows per route, if a route runs frequently enough (every 10 minutes, 8 AM to 8 PM, over a year). Of course, I can avoid refreshing the departures table if the schedule hasn’t changed, but still, preparing this table will not take a constant amount of time; e.g. it will depend on the schedule’s size.
>> Any tips appreciated!
>
> How about:
>
> SELECT
> *
> FROM
> generate_series ('2021-08-02 08:00:00'::timestamp, '2021-08-02 10:59:00'::timestamp, interval '90 minutes') AS instant
> UNION
> SELECT
> *
> FROM
> generate_series ('2021-08-03 08:00:00'::timestamp, '2021-08-03 20:00:00'::timestamp, interval '90 minutes') AS instant
> ORDER BY instant;

Yes, in fact, I wrote the following:

--------------------------------------------------------------------------------------------------------------------------

CREATE FUNCTION generate_series(tstzrange, interval) RETURNS SETOF timestamp with time zone AS $$
SELECT n
FROM generate_series(lower($1), upper($1), $2) AS t0(n)
WHERE $1 @> n
$$ LANGUAGE sql immutable;

CREATE FUNCTION generate_series(tsrange, interval) RETURNS SETOF timestamp without time zone AS $$
SELECT n
FROM generate_series(lower($1), upper($1), $2) AS t0(n)
WHERE $1 @> n
$$ LANGUAGE sql immutable;

That was the easy part. My end goal is to iterate over a tsmultirange: I would like to get each individual range from a given multi range. Ideally, I’d like to do that without parsing the textual version of the multi range.

While mowing the lawn, I thought that since the syntax of multi ranges is similar to arrays, maybe I could use unnest(), but sadly, that was not to be the case:

# select unnest('{[2021-08-02,2021-08-04],[2021-08-07,2021-08-09)}'::tsmultirange);
ERROR: function unnest(tsmultirange) does not exist
LINE 1: select unnest('{[2021-08-02,2021-08-04],[2021-08-07,2021-08-...

Apparently, PG can accept multi range values, but can’t do much with them at the time, except to check for inclusion/exclusion.

Thanks for your time!
François

>> François
>
>
> --
> Adrian Klaver
> adrian(dot)klaver(at)aklaver(dot)com <mailto:adrian(dot)klaver(at)aklaver(dot)com>