Why does function i PostgreSQL not raise exception? - postgresql

Question

I have a before insert or update trigger which is supposed to validate values of two columns in the inserted/updated data, raise an exception if the data are not valid or - if valid - add values to two other columns in the insert/update.
However, when I test with invalid data I get "ERROR: query has no destination for result data. HINT: If you want to discard the results of a SELECT, user PERFORM instead. CONTEXT: PL/pgSQL function before_insert_update() line 3 at SQL statement."
I have tried to read the PostgreSQL documentation and I have googled for explanations, but I just have to admin that my understanding of SQL is not sufficient to make it work.
My function is
CREATE or replace FUNCTION before_insert_update()
RETURNS trigger
LANGUAGE 'plpgsql'
COST 100
VOLATILE NOT LEAKPROOF
AS $BODY$
begin
select * from addresses
where addresses.roadname = NEW.roadname and
addresses.housenumber = NEW.housenumber;
if ##ROWCOUNT > 0 then
begin
select addresses.roadcode,
addresses.geom
into NEW.roadcode, NEW.geom
from addresses
where addresses.roadname = NEW.roadname and
addresses.housenumber = NEW.housenumber;
return NEW;
end;
else
declare _adresse text;
begin
_address := concat(NEW.roadname, ' ', NEW.housenumber);
raise exception 'The address does not exist: %', _address
using hint = 'Check the address here: https://danmarksadresser.dk/adresser-i-danmark/';
end;
end if;
END
$BODY$;
The trigger is pretty straight forward
BEFORE INSERT OR UPDATE
ON table
FOR EACH ROW
EXECUTE PROCEDURE before_insert_update();
What is it that I am doing wrong?

Answer 1

There is no need to run a test if the row is present. Just select it, and check the status afterwards:
CREATE or replace FUNCTION before_insert_update()
RETURNS trigger
LANGUAGE plpgsql
COST 100
VOLATILE NOT LEAKPROOF
AS
$BODY$
begin
select addresses.roadcode, addresses.geom
into NEW.roadcode, NEW.geom
from addresses
where addresses.roadname = NEW.roadname and
addresses.housenumber = NEW.housenumber;
if found then
return new;
end if;
raise exception 'The address does not exist: %', concat(NEW.roadname, ' ', NEW.housenumber)
using hint = 'Check the address here: https://danmarksadresser.dk/adresser-i-danmark/';
END
$BODY$;

Answer 2

Looks like you're trying to use SQL Server specific code in Postgres, which isn't going to work of course.
PL/pgSQL doesn't allow SELECTs just anywhere, when the result isn't passed to somehwere, like variables, etc.. And there is no ##ROWCOUNT. From what I can guess what you want to do, you can use EXISTS and your query for the condition of the IF.
CREATE
OR REPLACE FUNCTION before_insert_update()
RETURNS trigger
AS
$$
BEGIN
IF EXISTS(SELECT *
FROM addresses
WHERE addresses.roadname = new.roadname
AND addresses.housenumber = new.housenumber) THEN
SELECT addresses.roadcode,
addresses.geom
INTO new.roadcode,
new.geom
FROM addresses
WHERE addresses.roadname = new.roadname
AND addresses.housenumber = new.housenumber;
RETURN new;
ELSE
RAISE EXCEPTION 'The address does not exist: %', concat(new.roadname, ' ', new.housenumber)
USING HINT = 'Check the address here: https://danmarksadresser.dk/adresser-i-danmark/';
END IF;
END
$$
LANGUAGE plpgsql;