如何在SQL中使用引用具有两个主键的表的外键创建命令文件？

Question

我正在为我的数据库管理类做一个项目，我无法弄清楚如何为在SQL中创建的表创建一个文件命令。我们有两个实体和两个主键，我无法创建表。我想知道你是否有任何意见？旅行社表有两个主键，它们是这些表中的外键，由于某种原因，我无法获得这些表，因此我无法弄清楚。以下是我迄今：
这些是引用的表有两个主键的外键的表：

create table rental (rental_id integer not null, 
max_daily_mileage integer not null, 
is_unlimited_mileage char(3) not null, 
rental_start_date integer not null, 
rental_end_date integer not null, 
is_reservation_a_hold char(3), 
checked_out_mileage integer not null, 
checked_in_mileage integer not null, 
checked_out_condition char(8) not null, 
checked_in_condition char(8) not null, 
company_discount integer, 
reservation_is_cancelled char(3), 
employee_id_booked integer not null, 
employee_id_checked_out_car integer not null, 
employee_id_checked_in_car integer not null, 
discount_id integer not null, 
customer_id integer not null, 
class_id integer not null, 
car_id integer not null, 
franchise_id integer not null, 
company_id integer not null, 
primary key (rental_id), 
foreign key (discount_id) references frequent_renter_discount (discount_id), 
foreign key (customer_id) references customers (customer_id), 
foreign key (travel_agency_id) references travel_agency (travel_agency_id), 
foreign key (car_id) references car (car_id), 
foreign key (franchise_id) references franchise (franchise_id), 
foreign key (company_id) references company (company_id)); 

create table customers 
(customer_id integer not null, 
employer char(15) not null, 
id_verified integer, 
employee_id integer not null, 
corporate_account_id integer not null, 
credit_card_id integer not null, 
company_id integer not null, 
primary key (customer_id), 
foreign key (employee_id) references employees (employee_id), 
foreign key (corporate_account_id) references corporate_account (corporate_account_id), foreign key (credit_card_id) references credit_card (credit_card_id), 
foreign key (company_id) references company (company_id), 
foreign key (rental_id) references rental (rental_id)); 

表有两个主键：

create table travel_agency 
(travel_agency_id integer not null, 
travel_agent_id integer not null, 
location char(15) not null, 
company_id integer not null, 
primary key (travel_agency_id,travel_agent_id), 
foreign key (company_id) references company (company_id)); 

Answer 1

嗯，你只是不能仅在复合主键的一部分上添加FOREIGN KEY CONSTRAINT。 （顺便说一下，表租赁定义中没有字段travel_agency_id integer ...）

如果您想引用组合键PK，则必须添加对组成键的所有字段的引用。

这意味着，对于表租赁

CREATE TABLE rental (
rental_id integer not null, 
--..., 
travel_agency_id integer, 
travel_agent_id integer, 
PRIMARY KEY (rental_id), 
--..., 
FOREIGN KEY (travel_agency_id, travel_agent_id) 
    REFERENCES travel_agency(travel_agency_id, travel_agent_id) 
); 

或更改您的设计，使用了代理键，并添加一个唯一约束对哪些组合应该是唯一的字段，例如。

一般来说，我会尽量避免复合键。