create table Students(
id int identity(0,1),
namestud varchar(20) not null,
surnamestud varchar(20) NOT NULL,
studid int not null,
telegramid int not null,
course varchar(20) not null
)

alter table Students add constraint pk_stud primary key(id, course)



create table Courses(
course_c varchar(20) not null,
pass int not null
constraint pk_courses primary key(course_c)
)


create table Teachers(
telegramid_t int not null,
course_t varchar(20) not null
constraint pk_teachers primary key(course_t)
constraint fk_teachers foreign key(course_t) references Courses(course_c)
)

create table Grades(
id_g int not null,
course_g varchar(20) not null,
grade int not null,
attendance bit not null,
constraint fk_grades_students foreign key(id_g,course_g) references Students(id,course) on update cascade on delete cascade,
constraint fk_grades_teachers foreign key(course_g) references Teachers(course_t)
)


insert into Courses  (course_c, pass) values
('Матстат', 170526),
('Питон', 480248),
('Матанализ', 109583),
('БД', 150235)








drop table Grades;
drop table Students;
drop table Teachers;
drop table Courses;


select * from Students
select * from Teachers
select * from Grades
select * from Courses