如何在SQL中将表1中的复合主键引用为表2作为外键？

Question

我在创建指向其他表中的复合主键的外键时遇到问题。

CREATE TABLE CityCountry(
    city_code VARCHAR(5) NOT NULL,
    city VARCHAR(100),
    country_code VARCHAR(5) NOT NULL,
    country VARCHAR(100),
    citycountry_id VARCHAR(105) PRIMARY KEY (city_code, country_code) 
)

CREATE TABLE FlightRoute(
    flightroute_id INT IDENTITY(1, 1) PRIMARY KEY,
    flight_departureCountryCity VARCHAR(105),
    flight_id INT FOREIGN KEY 
        REFERENCES Flight(flight_id)
        ON DELETE NO ACTION
        ON UPDATE NO ACTION,
    flight_departureDateTime DATETIME,
    flight_arrivalDateTime DATETIME,
    aircraft_code VARCHAR(15) FOREIGN KEY 
        REFERENCES Aircraft(aircraft_code)
        ON DELETE NO ACTION
        ON UPDATE NO ACTION,
    flight_order SMALLINT
)

我在stackoverflow中尝试了解决方案，但没有解决

alter table flightroute add constraint FK_FlightRoute_CityCountry foreign key FlightRoute(flight_departureCountryCity) references CityCountry (city_code, country_code) 

Answer 1

为了创建外键，引用的列应该是PK或unique index 。 由于您已经拥有PK ，因此可以使您的列成为unique index ：

create unique index UI_CityCountry
   on CityCountry(citycountry_id); 

现在创建FK ：

alter table flightroute
add constraint FK_FlightRoute_CityCountry
foreign key (flight_departureCountryCity)
references CityCountry (citycountry_id) 

Answer 2

尝试像这样定义表：

CREATE TABLE CityCountry(
    citycountry_id VARCHAR(105) NOT NULL PRIMARY KEY,
    city_code VARCHAR(5) NOT NULL,
    city VARCHAR(100),
    country_code VARCHAR(5) NOT NULL,
    country VARCHAR(100)
);

CREATE TABLE FlightRoute(
    flightroute_id INT IDENTITY(1, 1) PRIMARY KEY,
    flight_departureCountryCity VARCHAR(105) FOREIGN KEY
        REFERENCES CityCountry(citycountry_id),
    flight_id INT FOREIGN KEY 
        REFERENCES Flight(flight_id)
        ON DELETE NO ACTION
        ON UPDATE NO ACTION,
    flight_departureDateTime DATETIME,
    flight_arrivalDateTime DATETIME,
    aircraft_code VARCHAR(15) FOREIGN KEY 
        REFERENCES Aircraft(aircraft_code)
        ON DELETE NO ACTION
        ON UPDATE NO ACTION,
    flight_order SMALLINT
);

也就是说，在第一个表中正确声明主键，然后在第二个表中使用它。

就个人而言，我更喜欢主键是递增的数值，但是我要保留原始类型。