我想使用“地址”表中的“邮政编码”作为主键，作为“客户”表中的外键。我从rentals表中获取'RentalID'作为'customers'表中的外键做了同样的事情，但是，当我尝试对'Postcode'做同样的事情时，它给了我这个错误：“请检查表上的外键约束父表地址的客户“。
请注意，我使用的是 khanacademy.org 上的在线 SQLite IDE
这是我的代码：
CREATE TABLE rentals
( RentalID INTEGER PRIMARY KEY, CarRegistration TEXT, DateHired TEXT,
DateReturned TEXT);
INSERT INTO rentals VALUES ( 1, "J986NDX", "12.2.94", "25.8.94");
INSERT INTO rentals VALUES ( 2, "K788NRT", "1.3.95", "1.4.96");
INSERT INTO rentals VALUES ( 3, "L346NDS", "2.4.96", "");
INSERT INTO rentals VALUES ( 4, "J986NDX", "15.9.94", "14.9.95");
INSERT INTO rentals VALUES ( 5, "M411NGT", "15.9.95", "1.2.96");
CREATE TABLE customers (CustomerID INTEGER, CustomerSurname TEXT,
Customerinitial TEXT, Companyname TEXT, Postcode TEXT, RentalID INTEGER ,
PRIMARY KEY(CustomerID, RentalID), FOREIGN KEY (RentalID) REFERENCES
rentals(RentalID), FOREIGN KEY (Postcode) REFERENCES address(Postcode));
INSERT INTO customers VALUES ( 153, "Nazarali", "N", "MF Plastics", "DB5
3ER", 1);
INSERT INTO customers VALUES ( 153, "Nazarali", "N", "MF Plastics", "DB5
3ER", 2);
INSERT INTO customers VALUES ( 187, "Brown", "L", "MF Plastics", "DB5 3ER",
3); INSERT INTO customers VALUES ( 287, "Pinner", "M", "Took Ltd", "DB6
8YU", 4); INSERT INTO customers VALUES ( 287, "Pinner", "M", "Took Ltd",
"DB6 8YU", 5);
CREATE TABLE address (Postcode TEXT PRIMARY KEY, town TEXT);
INSERT INTO address VALUES ( "DB5 3ER", "Derby");
INSERT INTO address VALUES ( "DB6 8YU", "Derby");
如何解决？