--创建一个course1
create table course1
(
  cno char(4) primary key,
  cname char(40),
  cpno char(4),
  ccredit smallint
);
go
--创建一个course2的外键为course1的cno
create table course2
    (
      cno char(4) primary key ,
      cname char(40) ,
      cpno char(4) ,
      ccredit smallint ,
      foreign key ( cpno ) references course1 ( cno )
    ) ;

------解决方案--------------------

Cpno少了小括号

create table Course
(
 Cno char(4) primary key,
 Cname char(40),
 Cpno char(4),
 Ccredit smallint,
 foreign key (Cpno) references Course(Cno)
);