create table department
(dept_name varchar(20) not null primary key,
building varchar(20),
budget numeric(12,2));
create table instructor
( ID varchar(5),
name varchar(20),
dept_name varchar(20),
salary numeric(12,1)
);
create table course
( course_id varchar(8),
title varchar(50),
dept_name varchar(20) references department,
credits numeric(2,0),
primary key (course_id)
#foreign key constraints can be here too :
#foreign key (dept_name) references department
);
/*alter table course
change column course_id
course_id varchar(8) unique;
*/
create table section
( course_id varchar(8),
sec_id varchar(8),
semster varchar(6),
year numeric(4,0),
building varchar(15),
room_number varchar(7),
time_sloth_id varchar(4),
primary key(course_id,semster,year),
foreign key (course_id) references course
);
create table teach
( ID varchar(5),
course_id varchar(8),
semster varchar(6),
year numeric(4,0),
primary key (ID,course_id,semster, year),
foreign key (ID) references instructor,
foreign key (course_id, semster, year) references section
);
这段代码运行在MySql上总是在create table section的时候报error 1215,不能添加外键......求问为什么啊......