-- Your SQL goes here

alter table kecheng
    rename column group_id to kecheng_teacher_id;

alter table kecheng
    alter column kecheng_teacher_id set not null;

alter table kecheng
    drop column teacher_id;

alter table kecheng
    rename to kecheng_student;

alter table kecheng_student
    add constraint kecheng_student_kecheng_teacher_id_fk
        foreign key (kecheng_teacher_id) references kecheng_teacher;