= UseCase3001 – Enroll in Subject

**Initiating actor:** Student

**Other actors:** Professor

**Description:**
A student wants to enroll in a subject offered by their faculty. The system checks prerequisites, enrollment limits, and records the enrollment in the database.

**Scenario:**

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

2. System displays a list of subjects available for their faculty:
{{{
SELECT s.Id, s.Name, s.Semester, s.Credits 
FROM Subject s 
JOIN Faculty f ON s.Faculty_Id = f.Id
JOIN Student st ON st.Faculty_Id = f.Id
WHERE st.Id = :student_id;
}}}

3. Student chooses a subject and clicks “Enroll.”

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

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

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