ITPEC FE Morning April 2022 Question 25

Many-to-Many Relationship Mapping — translate M:N relationship from ER diagram to relational tables.

To map a many-to-many relationship:

• •Create a table for each entity
• •Create a junction table (bridge table) containing the primary keys of both entities as foreign keys
• •The combination of both foreign keys typically forms the composite primary key of the junction table

Example: Students ↔ Courses → Enrollments(student_id, course_id)

Why not others:
- (a) Combine into single table — violates normalization, causes massive redundancy
- (b) Import PK from smaller to larger — works for one-to-many, not M:N
- (c) Import PK both ways — describes one-to-one or incorrect M:N implementation

Key rule: M:N always requires a third (junction) table; 1:N uses a foreign key in the "many" side table.

AI-generated — may contain errors