MySQL 创建外键的语法

Question

创建外键时这种语法是否正确？

create table department
(
  departmentID int not null auto_increment primary key,
  name varchar(30)
) type=InnoDB;

create table employee
(
  employeeID int not null auto_increment primary key,
  name varchar(80),
  job varchar(30),
  departmentID int not null references department(departmentID)
) type=InnoDB;

Answer 1

看起来 MySQL 接受它（不抱怨语法），但实际上并没有创建外键。

要创建此外键，请运行以下命令：

ALTER TABLE employee ADD CONSTRAINT fk_department FOREIGN KEY (departmentID) REFERENCES department (departmentID);

Answer 2

create table employee
(
  employeeID int not null auto_increment primary key,
  name varchar(80),
  job varchar(30),
  departmentID int not null ADD CONSTRAINT fk_department FOREIGN KEY (departmentID) references department(departmentID)
) 

Answer 3

FOREIGN KEY (departmentID) REFERENCES department(departmentID)

谢谢。！