2.4 a)
CREATE TRIGGER ExamInsert_after_ins
    ON Exam
    AFTER INSERT
AS
BEGIN

    DECLARE @size INT
    SELECT @size = count(*) FROM inserted

    if @size = 1
    BEGIN

        DECLARE @group VARCHAR(20), @count_stud INTEGER, @subject VARCHAR(255)
        SELECT @group = NameGroup FROM Student WHERE Id_Student in (SELECT Id_Student FROM inserted)
        SELECT @subject = Subject FROM inserted

        SELECT @count_stud = count(*) FROM Exam AS e WHERE e.Id_Student
            in (SELECT Id_Student FROM Student WHERE NameGroup = @group) AND Subject = @subject

        DECLARE @cortage_count INT
        SELECT @cortage_count = count(*) FROM Exam_Group AS e WHERE e.Subject = @subject

        IF @cortage_count = 0
            INSERT INTO Exam_Group VALUES(@group, @subject, @count_stud)
        ELSE
            UPDATE Exam_Group SET Count = @count_stud WHERE Subject = @subject AND NameGroup = @group


    END
    ELSE BEGIN
        PRINT 'ошибка'
        ROLLBACK TRAN
    END
END