代码如下:
create table classroom
(building varchar(15),
room_number varchar(7),
capacity numeric(4,0),
primary key (building, room_number)
);create table department
(dept_name varchar(20),
building varchar(15),
budget numeric(12,2) check (budget > 0),
primary key (dept_name)
);create table course
(course_id varchar(8),
title varchar(50),
dept_name varchar(20),
credits numeric(2,0) check (credits > 0),
primary key (course_id),
foreign key (dept_name) references department
on delete set null
);书上的示例代码,可是我用MySQL创建表时提示:Cannot add foreign key constraint.
请问这个问题该怎么解决呢?谢谢!
create table classroom
(building varchar(15),
room_number varchar(7),
capacity numeric(4,0),
primary key (building, room_number)
);create table department
(dept_name varchar(20),
building varchar(15),
budget numeric(12,2) check (budget > 0),
primary key (dept_name)
);create table course
(course_id varchar(8),
title varchar(50),
dept_name varchar(20),
credits numeric(2,0) check (credits > 0),
primary key (course_id),
foreign key (dept_name) references department
on delete set null
);书上的示例代码,可是我用MySQL创建表时提示:Cannot add foreign key constraint.
请问这个问题该怎么解决呢?谢谢!
(course_id varchar(8),
title varchar(50),
dept_name varchar(20),
credits numeric(2,0) check (credits > 0),
primary key (course_id),
foreign key (dept_name) references department(dept_name)
on delete set null
);
(course_id varchar(8),
title varchar(50),
dept_name varchar(20),
credits numeric(2,0) check (credits > 0),
primary key (course_id),
foreign key (dept_name) references department(dept_name)
on delete set null
);