Simple to use Oracle triggers

--Build table statements
CREATE TABLE Student (ID number (9), name VARCHAR2 (+), age number (5));CREATE TABLE Class (ID number (9), name VARCHAR2, Teacherid number (9), StudentID number (9));CREATE TABLE Teacher (ID number (9), name VARCHAR2 (+), age number (5));--Student InformationInsert  intoStudentValues(1,'YANGML', at);Insert  intoStudentValues(2,'Zhangj', at);Insert  intoStudentValues(3,'Zhulj', -);Insert  intoStudentValues(4,'CHENGLP', -);--Teacher InformationInsert  intoTeacherValues(1,'Yangls', -);Insert  intoTeacherValues(2,'Zhangls', -);Insert  intoTeacherValues(3,'Zhuls', -);Insert  intoTeacherValues(4,'Chenls', -);--class InformationInsert  intoClassValues(1,'First Grade',1,1);Insert  intoClassValues(2,'Second Grade',2,2);Insert  intoClassValues(3,'Third grade',3,3);Insert  intoClassValues(4,'Grade Four',4,4);--Delete TriggerCreate or Replace TriggerTrigdel beforeDelete  onclass forEach rowDeclare  --Local Variables herebegin   Delete  fromTeacherwhereTeacher.id=: old.id; Delete  fromStudentwhereStudent.id=: old.id;EndTrigdel;--Test DeleteDelete  fromclass;Select *  fromclass;Select *  fromstudent;Select *  fromTeacher