Ralat kekangan MySQL FOREIGN KEY

Question

Create table Student
(
    Sno varchar(7) primary key,
    Sname varchar(10) not null,
    Ssex char (2) check(Ssex=‘男’or Ssex=’女’),
    Sage int check(Sage between 15 and 45),
    Sdept varchar(20) default ‘计算机系’
);

Create table course
(
    Cno varchar(10) primary key,
    Cname varchar(20) not null,
    Ccredit int check(Sctedit>0),
    Semester int check(Semester>0),
    Period int check(Period>0)
);

Create table SC
(
    Sno varchar(7) foreign key references student(Sno),
    Cno varchar(10) foreign key references course(Cno),
    Grade int check(Grade between 0 and 100),
    Primary key (Sno,Cno)
);

Dua yang pertama berjaya mencipta jadual, tetapi yang ketiga melaporkan ralat:

Tukar yang ketiga:

Create table SC
(
    Sno varchar(7),
    Cno varchar(10),
    Grade int check(Grade between 0 and 100),
    foreign key (Sno) references student(Sno),
    foreign key (Cno) references course(Cno),
    Primary key (Sno,Cno),
);

Masih melaporkan ralat:

Sila jawab, terima kasih bos!

Answer 1

Cara mencipta kunci asing adalah salah,