嗨，我有麻烦做一个左连接，输出所有客户谁还没有下订单。我得到一个转换错误，并试图使用铸造转换，但它不工作。任何帮助都将不胜感激
以下是我的表格和数据：`
创建表customers（cust\u code varchar（2）主键，[first\u name]varchar（30）not null，last\u name varchar（30）not null，address varchar（100）not null，city varchar（35）not null）

create table Cust_Order(
order_no int ,
Cust_code varchar(2) not null,
order_date date not null, 
meth_pmt varchar(30) not null,
constraint Ord_order_no_pk primary key(order_no),
constraint Cus_cust_code_fk foreign key(Cust_code) references Customers)

create table Product(
product_id int ,
product_name varchar(100) not null,
product_price decimal(8, 2) not null,
constraint Pro_product_id_pk primary key(product_id))

create table Order_Line(
order_no int ,
product_id int ,
qty int not null,
sale_price decimal(8,2) not null,
constraint Ord_order_no_product_id_pk primary key(order_no, product_id),
constraint Pro_product_id_fk foreign key(product_id) references Product)

insert into Customers (Cust_code, [first_name], last_name, address, city)
values('A1', 'Kath', 'Morgan','122 Lilain Street', 'Palmerston North'),
  ('A2','Mike','Smith','67 Golf Hill Drive','Wellington'),
  ('A3','Glen','Hoddle','San Quentin Ave','Palmerston North'),
  ('A4','Dan','Boone','Alamo Road','Wellington')

insert into Cust_Order (order_no, Cust_code, order_date, meth_payment)
values(1, 'A1','2014-01-16','CC'),
    (2, 'A1','2014-02-16','CC'),
    (3, 'A2','2014-01-16','CHEQUE'),
    (4, 'A3','2014-03-17','CC')

insert into Product (product_id, product_name, product_price)
values(1, 'Network Card', 58.00),
    (2, 'Motherboard', 150.00),
    (3, 'Video Card', 232.00)

insert into Order_Line (order_no, product_id, qty, sale_price)
values(1,1,3,70.00),
    (1,2,1,170.00),
    (1,3,2,300.00),
    (2,1,2,70.00),
    (2,3,1,300.00),
    (3,1,2,70.00),
    (4,1,3,70.00)

我的select语句使用left join，它应该输出一个没有下订单的客户

select first_name + last_name as 'Customers who have not made an order', 
order_no from Customers as c
left join Cust_Order as o
on c.Cust_code = o.order_no 
where order_no is null