Question

所以我有一个多对多的关系数据库，现在我正处于建立数据库的阶段。

我正在使用mariadb，并且已阅读到在处理M：M时，最好有一个中间表来存储关系。我正在尝试这样做，但是我太笨了，以至于我无法找出创建列的正确语法？

CREATE TABLE doctor_hospitals (
    doctor_id INT FOREIGN KEY (doctor_id) REFERENCES doctors(id),
    hospital_id INT FOREIGN KEY (hospital_id) REFERENCES hospitals(id)
    ) ENGINE = InnoDB;

上面产生错误：

查询1错误：您的SQL语法有错误；检查与您的MariaDB服务器版本相对应的手册以获取正确的语法，以在'FOREIGN KEY（doctor_id）附近使用引用doctors（id），第2行的hospital_id INT FOREIGN KEY'

同时：

CREATE TABLE doctor_hospitals (
    FOREIGN KEY (doctor_id) REFERENCES doctors(id),
    FOREIGN KEY (hospital_id) REFERENCES hospitals(id)
    ) ENGINE = InnoDB;

产生错误：

查询1错误：一个表必须至少具有1列

这种排序很有道理。这是我要创建的内容：

CREATE TABLE doctors (
    id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
    userID VARCHAR(100) NOT NULL,
    first_names VARCHAR(100) NOT NULL,
    last_names VARCHAR(100) NOT NULL,
    medical_number INT NOT NULL,
    email VARCHAR(20) NOT NULL,
    country VARCHAR(20) NOT NULL,
    province VARCHAR(20) NOT NULL,
    city VARCHAR(20)) ENGINE = InnoDB;

CREATE TABLE hospitals (
    id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(150) NOT NULL,
    address1 VARCHAR(75),
    address2 VARCHAR(75),
    phone_number INT,
    country VARCHAR(15),
    province VARCHAR(15),
    city VARCHAR(20),
    zip_code VARCHAR(15)) ENGINE = InnoDB;

CREATE TABLE doctor_hospitals (
    doctor INT FOREIGN KEY (doctor_id) REFERENCES doctors(id),
    hospital INT FOREIGN KEY (hospital_id) REFERENCES hospitals(id)
    ) ENGINE = InnoDB;

感谢您的帮助！

Answer 1

FK是约束。您需要首先定义列。还需要为FK定义索引。

CREATE TABLE doctor_hospitals (
    doctor_id INT UNSIGNED  NOT NULL,
    hospital_id INT UNSIGNED  NOT NULL,
    PRIMARY KEY (doctor_id,hospital_id),
    KEY IX_doctor_hospitals_hospital_id(hospital_id),
    CONSTRAINT FK_doctor_hospitals_hospitals FOREIGN KEY (hospital_id) REFERENCES hospitals(id),
    CONSTRAINT FK_doctor_hospitals_doctors FOREIGN KEY (doctor_id) REFERENCES doctors(id)
    ) ENGINE = InnoDB;

如何为M：M数据库创建中间表

1 个答案: