Add recurrent actions for defined period in Postgresql - postgresql

Question

Beside of unique actions we need recurrent actions in our database. We wan't the user to be able to define a periodicity (all 1,2,3,.. years) and a period (e.g. from 2018 - to 2020) in a form. This data should be used to insert appropriat datasets for a defined action.
If the user chooses an annual periodicity starting from 2018 3 datasets (2018, 2019 and 2020) should be inserted in the actions table.
If the user chooses an biannual periodicity starting from 2018 only 2 datasets (2018 and 2020) should be inserted in the actions table.
The simplified table actions looks like this:
id serial not null
id_action integer
action_year integer
periodicity integer
from_ integer
to_ integer
I need a starting point for the sql statement.

Answer 1

You should use generate_series(start, stop, step)
Annual:
=> select generate_series(2018,2020,1);
generate_series
-----------------
2018
2019
2020
(3 rows)
Biannual:
=> select generate_series(2018,2020,2);
generate_series
-----------------
2018
2020
(2 rows)

Answer 2

I didn't knew the function generate_series() until now. Thanks to point me in that direction.
To get things running like I intended I need to use the generate_series() inside an Trigger function that is fired AFTER INSERT. After first running into troubles with recursive Trigger inserts I now have the problem, that my Trigger produces to many duplicate inserts (increasing with the choosen periodicity).
My table actions looks like this:
id serial not null
id_action integer
action_year integer
periodicity integer
from_ integer
to_ integer
My Trigger on the table:
CREATE TRIGGER tr_actions_recurrent
AFTER INSERT
ON actions
FOR EACH ROW
WHEN ((pg_trigger_depth() = 0))
EXECUTE PROCEDURE actions_recurrent();
Here my trigger function:
CREATE OR REPLACE FUNCTION actions_recurrent()
RETURNS trigger AS
$BODY$
BEGIN
IF NEW.periodicity >0 AND NEW.action_year <= NEW.to_-NEW.periodicity THEN
INSERT into actions(id_action, action_year,periodicity, from_, to_)
SELECT NEW.id_action, y, NEW.periodicity, NEW.from_, NEW.to_
FROM actions, generate_series(NEW.from_+NEW.periodicity,NEW.to_,NEW.periodicity) AS y;
END IF;
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
When I'm doing an insert
INSERT INTO actions (id_action, action_year,periodicity,from_, to_)
VALUES (50,2018,4,2018,2028);
I get one row for action_year 2018, but 13 rows 2022 and 2026??
In my understanding, the IF-clause in the trigger-function should avoid such a repetitive execution.