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

------解决方案--------------------
create table Course (
Cno char(4) primary key,
Cname char(40),
Cpno char(4) references Course(Cno),Ccredit smallint,  
)

------解决方案--------------------
SQL code

create table Course (Cno char(4) primary key,Cname char(40),Cpno char(4),Ccredit smallint,foreign key [color=#FF0000](Cpno)[/color] references Course(Cno));