Add trigger to automatically calculate subtotal price of cart

shop.sql

@@ -130,4 +130,18 @@ begin
 	where id = old.cart_id;
 end;
 //
-delimiter;
+delimiter;
+
+delimiter //
+create trigger calculate_price_subtotal
+before insert on cart_item
+for each row
+begin
+	set new.price_subtotal = (
+		select new.count * p.price_pc
+		from product p
+		where p.id = new.product_id
+	);
+END;
+//
+DELIMITER ;