enter image description here我无法为表创建外键约束

无法创建外键约束

CREATE TABLE dept ( DNO INT NOT NULL primary key,DNAME varchar(15) not null,Location varchar(15) not null,NumEmp int not null,Managers int not null,Foreign key (DNO) references employee (DNO) );

create table employee ( Ssn CHAR(9) NOT NULL primary key,FNAME VARCHAR(15) NOT NULL,MINIT VARCHAR(5),LNAME VARCHAR(15) NOT NULL,bdaTE DATE,ADDRESS VARCHAR(30),SEX CHAR,SALARY DECIMAL(10,2),SUPERSsn CHAR(9),DNO INT NOT NULL )