oracle 数据库插入问题

CREATE TABLE Tb_Dept
  (DeptId Char(2) Primary Key NOT NULL,
  DeptName VarChar2(20)NOT NULL
  );

 CREATE TABLE Tb_TeachingYear
  (TeachingYearId Char(4) Primary Key NOT NULL,
  TeachingYearName VarChar2(13) NOT NULL
  );

CREATE TABLE Tb_Term
  (TermId Char(2) Primary Key NOT NULL,
  TermName VarChar2(8) NOT NULL
  );


 CREATE TABLE Tb_Class
  (
  ClassId char(7) NOT NULL Primary key,
  ClassName VarChar2(20) NOT NULL ,
  DeptId char(2) NOT NULL REFERENCES Tb_Dept(DeptId) ,
  StuNumber number DEFAULT '0' NOT NULL 
  );

CREATE TABLE Tb_Student
  (
  StuId char(9) NOT NULL primary key,
  StuName VarChar2(8) NOT NULL,
  ClassId char(7) NOT NULL REFERENCES Tb_Class,
  Sex char(1) DEFAULT 'M' NOT NULL CHECK (Sex IN ('M','F')),
  Birthday date NOT NULL
  );


 CREATE TABLE Tb_Course
  (CourseId char(6) NOT NULL primary key,
  CourseName varchar2(30) NOT NULL,
  Deptid char(2) NOT NULL REFERENCES Tb_Dept(DeptId ),
  CourseGrade real DEFAULT '0' NOT NULL CHECK (CourseGrade>=0 and CourseGrade<100)  
  );


CREA