postgres, add row when a value is missing - sql

Question

Forgive what may be a silly question, but I'm not much of a database guru.
I have a table with three columns. Here's a sample:
stationtest | id_date | val_no3
------------+-------------+---------
27 | 1 |
27 | 2 | 7
27 | 25 |
27 | 50 | 8
27 | 75 | 9
27 | 100 | 10
30 | 1 |
30 | 14 | 7
30 | 25 |
30 | 65 | 8
30 | 75 | 9
30 | 100 | 10
I would like to have a new table that have one row for each value id_date missing and it combines stationtest number,
like this one :
stationtest | id_date | val_no3
------------+-------------+---------
27 | 1 |
27 | 2 | 7
27 | 3 |
27 | 4 |
27 | 5 |
27 | 6 |
27 | (...) |
27 | 25 |
27 | 26 |
27 | 27 |
27 | (...) |
27 | 50 | 8
27 | (...) |
27 | 75 | 9
27 | (...) |
27 | 98 |
27 | 99 |
27 | 100 | 10
30 | 1 |
30 | 2 | 7
30 | 3 |
30 | 4 |
30 | 5 |
30 | 6 |
30 | (...) |
30 | 25 |
30 | 26 |
30 | 27 |
30 | (...) |
30 | 50 | 8
30 | 75 | 9
30 | (...) |
30 | 98 |
30 | 99 |
30 | 100 | 10
I have this query but i don't know how to make it work for each stationtest :
insert into tabletest (id_date)
select i
from generate_series(1, (select max(id_date) from tabletest)) i
left join tabletest on tabletest.id_date = i
where tabletest.id_date is null;
It is possible ? Thank you for help.

Answer 1

Try this:
DO $$
DECLARE
st_test integer;
i integer;
BEGIN
FOR st_test in (SELECT distinct stationtest FROM tabletest) LOOP
EXECUTE 'INSERT INTO test(stationtest, id_date) SELECT $1 as stationtest, generate_series as id_date FROM generate_series((SELECT min(id_date) FROM test), (SELECT max(id_date) FROM test))' USING st_test;
END LOOP;
END;
$$;
I don't have the data handy, but the general format should work.