create or replace function trigf1() returns trigger as $$
begin
if (ballotbox.totvoters>votes.nofvotes) then
raise notice 'more voters than allowed';
return old;
else return new;
end if;
end;
$$ language plpgsql;

create trigger T1
Before insert or update on votes
for each row
execute procedure trigf1();

ERROR:  missing FROM-clause entry for table "ballotbox"
LINE 1: SELECT (ballotbox.totvoters > votes.nofvotes)
                ^
QUERY:  SELECT (ballotbox.totvoters > votes.nofvotes)
CONTEXT:  PL/pgSQL function trigf1() line 3 at IF

create table ballotBox
(bno integer,
cid numeric(4,0),
street varchar(20),
hno integer,
totvoters integer,
primary key (bno),
foreign key (cid) references city);

create table votes
(cid numeric(4,0),
bno integer,
pid numeric(3,0),
nofvotes integer,
foreign key (cid) references city,
foreign key (bno) references ballotBox,
foreign key (pid) references party,
check (nofvotes >= 0));

insert into ballotBox values
(1, 1, 'street1', 10, 1500),
(2, 1, 'street2', 15, 490),
(3, 1, 'street2', 15, 610),
(4, 1, 'street2', 15, 650),
(5, 2, 'street3', 10, 900),
(6, 2, 'street3', 55, 800),
(7, 2, 'street4', 67, 250),
(8, 2, 'street4', 67, 990),
(9, 2, 'street5', 5, 600),
(10, 3, 'street1', 72, 1000),
(11, 3, 'street6', 25, 610),
(12, 3, 'street6', 25, 600),
(13, 4, 'street2', 3, 550),
(14, 4, 'street7', 15, 500),
(15, 5, 'street8', 44, 1100),
(16, 5, 'street9', 7, 710),
(17, 5, 'street10', 13, 950);

insert into votes values
(1, 1, 200, 100),
(1, 1, 210, 220),
(1, 1, 220, 2),
(1, 1, 230, 400),
(1, 1, 240, 313),
(1, 1, 250, 99),
(2, 1, 200, 55),
(2, 1, 210, 150),
(2, 1, 220, 2),
(2, 1, 230, 16),
(2, 1, 240, 210);