CREATE OR REPLACE FUNCTION trigf1()
  RETURNS trigger AS
$$
BEGIN
    IF EXISTS (SELECT *
        FROM sells join receipt on sells.license=receipt.license
         WHERE iname = new.iname and new.cid = receipt.cid and new.rno = receipt.rno
        ) THEN
RETURN new; -- checks if item iname is equal to the insert item and if in table sells license equal to the license in table receipt.
    ELSE
RAISE NOTICE 'This Cafe Not selling %s item',new.iname;
RETURN null;
END IF;
END;
$$
LANGUAGE 'plpgsql';

CREATE or replace TRIGGER T1
BEFORE INSERT
ON buys
FOR EACH ROW
EXECUTE PROCEDURE trigf1();