SQL is Agile(lucumr.pocoo.org)

  create table quote(
    quote_id int8 primary key,
    customer_id int8,
    valid daterange
  );
  
  create table quote_line(
    quote_id int8 references quote(quote_id),
    amount numeric(10,2)
  );
  
  create or replace function check_quote() returns trigger language plpgsql as $$
  declare
    line_count int;
    line_sum numeric;
  begin
    select into line_count, line_sum
      count(*), sum(amount) from quote_line where quote_id=NEW.quote_id;
    if (line_count < 1 OR line_sum < 0 OR line_sum > 1000000)
    then raise exception 'invalid quote';
    else return NEW;
    end if;
  end;
  $$;
  
  create constraint trigger quote_check_trig after insert or update or delete on quote deferrable initially deferred for each row execute procedure check_quote();
  create constraint trigger quote_line_check_trig after insert or update or delete on quote_line deferrable initially deferred for each row execute procedure check_quote();