= UseCase3001 – Enroll in Subject

**Initiating actor:** Student

**Other actors:** None

**Description:**
A student enrolls in a subject offered by their faculty and selects a specific professor who teaches that course instance.

**Scenario:**

1. Student logs into the system and selects “Enroll in Subject.”

2. System displays available subjects and the professors teaching them at the student's faculty:
{{{
SELECT s.Id AS Subject_Id, s.Name AS Subject_Name, p.Id AS Professor_Id, p.Name AS Professor_Name, p.Surname AS Professor_Surname
FROM Subject s
JOIN Professor p ON p.Faculty_Id = s.Faculty_Id
JOIN Student st ON st.Faculty_Id = s.Faculty_Id
WHERE st.Id = :student_id;
}}}

3. Student chooses a subject and the desired professor, then clicks “Enroll.”

4. System checks if the student is already enrolled in this subject:
{{{
SELECT * FROM Student_Subject
WHERE Student_Id = :student_id AND Subject_Id = :subject_id;
}}}

5. If not enrolled, system inserts the enrollment record:
{{{
INSERT INTO Student_Subject(Student_Id, Subject_Id, Professor_Id, Status, Enrollment_Date, Absences_Count) 
VALUES (:student_id, :subject_id, :professor_id, 'PASSED', :enrollment_date, 0);
}}}

6. System confirms enrollment and updates student's schedule.