Триггер для подсчёта стоимости всего заказа

CREATE OR REPLACE TRIGGER price
before INSERT OR UPDATE OF price_zakaz ON zakaz
FOR each ROW
DECLARE
price_tovar tovar.price%TYPE;
price_uslug uslugi.price%TYPE;
BEGIN
 SELECT price INTO price_tovar
  FROM tovar
  WHERE tovar.id_tovar=:NEW.id_tovar;
 
 SELECT price INTO price_uslug
  FROM uslugi inner join zakaz_uslugi ON
  uslugi.id_uslugi=zakaz_uslugi.id_uslugi
  
  WHERE zakaz_uslugi.id_zakaz=:NEW.id_zakaz;
 
:NEW.price_zakaz:=price_uslug*zakaz_uslugi.kol_vo_zakaz+price_tovar;
END;

CREATE TABLE tovar
(id_tovarnumber(3) CONSTRAINT pk_tovar PRIMARY KEY,
name_tovar VARCHAR2(150) NOT NULL,
price NUMBER(5) NOT NULL
)

CREATE TABLE uslugi
(
id_uslugi NUMBER(3) CONSTRAINT pk_uslugi PRIMARY KEY,
name_uslugi VARCHAR2(50) NOT NULL,
price NUMBER(5) NOT NULL
)

CREATE TABLE zakaz
(
id_zakaz NUMBER(3) CONSTRAINT pk_zakaz PRIMARY KEY,
date_zakaz DATE NOT NULL,
id_client NUMBER(3) NOT NULL,
id_tovar NUMBER(3) NOT NULL,
price_zakaz NUMBER(5),
id_discont NUMBER(3),
CONSTRAINT fk_id_client foreign KEY(id_client) references client(id_client) ON DELETE CASCADE,
CONSTRAINT fk_tovar foreign KEY(id_tovari) references tovar(id_tovar) ON DELETE CASCADE,
CONSTRAINT fk_discont foreign KEY(id_discont) references discont(id_discont) ON DELETE CASCADE
)

CREATE TABLE zakaz_uslugi
(
id_zakaz NUMBER(3) NOT NULL,
id_uslugi NUMBER(3) NOT NULL,
kol_vo_zakaz NUMBER(3) NOT NULL,
price_uslugi NUMBER(5),
CONSTRAINT pk_zakaz_uslugi PRIMARY KEY(id_zakaz,id_uslugi),
CONSTRAINT fk_id_zakaz foreign KEY(id_zakaz) references zakaz(id_zakaz) ON DELETE CASCADE,
CONSTRAINT fk_id_uslugi foreign KEY(id_uslugi) references uslugi(id_uslugi) ON DELETE CASCADE
)