create or replace function f ()
returns table (a bigint, b bigint, c bigint) as $$
declare
  r record;
begin
  for r in
    select ... from t1
  loop
    if (r.b is null) then
      for r in
        select ... from t2
      loop
        a = r.a; b = r.b; c = r.c;
        return next;
      end loop;
    else
      a = r.a; b = r.b; c = r.c;
      return next;
    end if;
  end loop;
end; $$ language plpgsql;

select ... from table into :variable, :variable, ...

IF (TG_OP = ’INSERT’) THEN
IF (TG_OP = ’UPDATE’) THEN
IF (TG_OP = ’DELETE’) THEN

create function F() returns trigger as $$
begin
  if (tg_op = 'INSERT' or tg_op = 'UPDATE') then
    new.column = value;
    return new; -- тут?
  end if;
  return new; -- или тут?
end; $$ language plpgsql;