我不知道为什么会出现无法添加外键约束错误

Question

我正在研究一个项目的架构，并尝试将其导入本地主机，这样我就可以编写一些查询，将数据库中的信息提取到网页上。我收到#1215 - Cannot add foreign key constraint 错误，它与使用cities(city_id) 作为外键有关。我不确定问题出在哪里，它们都是相同的数据类型（INT），city_id 是cities 表的主键。我被难住了，我希望这里有人可以伸出援手。

已编辑：所以我得到了这个工作，但没有订单表，我将粘贴在工作模式下方。

DROP TABLE IF EXISTS cities;
-- Table for storing cities
create table cities (
    city_id INT(100) NOT NULL AUTO_INCREMENT,
    city_name VARCHAR(32),
    PRIMARY KEY(city_id)
)ENGINE=InnoDB;

DROP TABLE IF EXISTS drivers;
-- table for Drivers registered in lyft database
create table drivers (
    driver_id INT(100) NOT NULL AUTO_INCREMENT,
    fname VARCHAR(32),
    lname VARCHAR(32),
    address VARCHAR(32),
    contactnumber VARCHAR(32),
    driver_city INT(100),
    PRIMARY KEY(driver_id),
    FOREIGN KEY (driver_city) REFERENCES cities(city_id)
)ENGINE=InnoDB;

DROP TABLE IF EXISTS cars;
-- Table for storing cars information in lyft
create table cars (
    car_id INT(100) NOT NULL AUTO_INCREMENT,
    car_name VARCHAR(32),
    car_type VARCHAR(32),
    car_model VARCHAR(32),
    car_licencenumber VARCHAR(32),
    PRIMARY KEY(car_id)
)ENGINE=InnoDB;


DROP TABLE IF EXISTS customers;
-- Table for storing customers using lyft
create table customers (
    c_id INT(100) NOT NULL AUTO_INCREMENT,
    c_fname VARCHAR(32),
    c_lname VARCHAR(32),
    c_city INT(100),
    PRIMARY KEY (c_id),
    FOREIGN KEY (c_city) REFERENCES cities(city_id)
)ENGINE=InnoDB;

DROP TABLE IF EXISTS owns;
--  Table stores which drivers are having which cars
create table owns (
    driver INT(100),
    car INT(100),
    PRIMARY KEY (driver,car),
    FOREIGN KEY (driver) REFERENCES drivers(driver_id) ON DELETE CASCADE,
    FOREIGN KEY (car) REFERENCES cars(car_id) ON DELETE CASCADE
)ENGINE=InnoDB;

我无法添加到数据库的表如下：

DROP TABLE IF EXISTS order;
-- Table stores which drivers are driving a customer
create table order (
    driver INT(100),
    customer INT(100),
    city INT(100),
    PRIMARY KEY (driver, customer, city),
    FOREIGN KEY (driver) REFERENCES drivers(driver_id),
    FOREIGN KEY (customer) REFERENCES customers(c_id),
    FOREIGN KEY (city) REFERENCES cities(city_id)
)ENGINE=InnoDB;

当尝试通过phpmyadmin 添加它时，我收到以下错误：

Static analysis:

2 errors were found during analysis.

    An expression was expected. (near "ORDER" at position 21)
    Unrecognized keyword. (near "ORDER" at position 21)

SQL query:

DROP TABLE IF EXISTS ORDER

MySQL said: Documentation
#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ORDER' at line 1

最终编辑：我终于想通了，我的问题是 order 是 mysql 中的保留/关键字，所以会引发错误。我将其更改为orders，一切都很好。我将在下面发布最终架构，以防有人遇到和我一样的麻烦。

DROP TABLE IF EXISTS cities;
-- Table for storing cities
create table cities (
    city_id INT(100) NOT NULL AUTO_INCREMENT,
    city_name VARCHAR(32),
    PRIMARY KEY(city_id)
)ENGINE=InnoDB;

DROP TABLE IF EXISTS drivers;
-- table for Drivers registered in lyft database
create table drivers (
    driver_id INT(100) NOT NULL AUTO_INCREMENT,
    fname VARCHAR(32),
    lname VARCHAR(32),
    address VARCHAR(32),
    contactnumber VARCHAR(32),
    driver_city INT(100),
    PRIMARY KEY(driver_id),
    FOREIGN KEY (driver_city) REFERENCES cities(city_id)
)ENGINE=InnoDB;

DROP TABLE IF EXISTS cars;
-- Table for storing cars information in lyft
create table cars (
    car_id INT(100) NOT NULL AUTO_INCREMENT,
    car_name VARCHAR(32),
    car_type VARCHAR(32),
    car_model VARCHAR(32),
    car_licencenumber VARCHAR(32),
    PRIMARY KEY(car_id)
)ENGINE=InnoDB;


DROP TABLE IF EXISTS customers;
-- Table for storing customers using lyft
create table customers (
    c_id INT(100) NOT NULL AUTO_INCREMENT,
    c_fname VARCHAR(32),
    c_lname VARCHAR(32),
    c_city INT(100),
    PRIMARY KEY (c_id),
    FOREIGN KEY (c_city) REFERENCES cities(city_id)
)ENGINE=InnoDB;

DROP TABLE IF EXISTS owns;
--  Table stores which drivers are having which cars
create table owns (
    driver INT(100),
    car INT(100),
    PRIMARY KEY (driver,car),
    FOREIGN KEY (driver) REFERENCES drivers(driver_id) ON DELETE CASCADE,
    FOREIGN KEY (car) REFERENCES cars(car_id) ON DELETE CASCADE
)ENGINE=InnoDB;

DROP TABLE IF EXISTS orders;
-- Table stores which drivers are driving a customer
create table orders (
    driver INT(100),
    customer INT(100),
    city INT(100),
    PRIMARY KEY (driver, customer, city),
    FOREIGN KEY (driver) REFERENCES drivers(driver_id),
    FOREIGN KEY (customer) REFERENCES customers(c_id),
    FOREIGN KEY (city) REFERENCES cities(city_id)
)ENGINE=InnoDB;

Answer 1

根据错误Cannot resolve table name，我猜您在创建表cities 之前尝试创建表drivers，这意味着您引用的表不存在。所以解决办法是先创建表cities