Trigger to reshape phonenumber - postgresql

Question

I want a trigger is my database which changes the first zero of a phone number to the appropriate country-code (in my case it's +31). My code so far is:
create or replace function correct_number()
returns trigger as $$
declare
Pnumber integer;
begin
select substring(phone, 1, 1) from "user" where phone = new.phone into Pnumber;
if Pnumber = 0 then
update "user"
set phone = overlay("user".phone placing '+31' from 1 for 1)
where id = new.id;
return null;
end if;
end
$$ language plpgsql;
create trigger force_countrynr
before insert on "user"
for each statement execute procedure correct_number();
There problem is that every time I try to add data, my DBMS gives an error that the end of the procedure is reached without a return. This means obviously that it doesn't consider the if-statement to be true, but I can't figure out why.
This is the DDL of the attribute that my function concerns is a varchar(13) and the my testquery is as follows:
insert into gebruiker
values('U5', 'Hans', '12345', 'Hans', null, 'Kraay', 'Hansworst', '0000QW', 'beukenweg', '4', null, '0612345678', 'test#notnow.nl', '2015-12-12');
I've tried changing the datatype of the zero in my if-statement, changing the datatype of the number-variable and many things more, but I can't get it to work.

Answer 1

You want to correct the number in each inserted row, so the trigger should be for each row.
There is no reason to query the table in the trigger, as the currently inserted row is available in the new variable.
There is no reason to update the table, just modify the new record and return it.
create or replace function correct_number()
returns trigger as $$
begin
if left(new.phone, 1) = '0' then
new.phone:= '+31' || right(new.phone, -1);
end if;
return new;
end
$$ language plpgsql;
create trigger force_countrynr
before insert on "user"
for each row execute procedure correct_number();