How can a many-to-many relationship be implemented in a database or ORM?

A many-to-many relationship in a database is implemented through an intermediate table (join table), which contains foreign keys to both related tables. For example, if there are tables Students and Courses, a Student_Course table is created with fields student_id and course_id.

In ORM, such as in Java using JPA/Hibernate, this can be implemented with the @ManyToMany annotation and specifying the join table with @JoinTable.

Example:

@Entity
public class Student {
    @Id
    private Long id;

    @ManyToMany
    @JoinTable(
        name = "student_course",
        joinColumns = @JoinColumn(name = "student_id"),
        inverseJoinColumns = @JoinColumn(name = "course_id")
    )
    private Set<Course> courses = new HashSet<>();
}

@Entity
public class Course {
    @Id
    private Long id;

    @ManyToMany(mappedBy = "courses")
    private Set<Student> students = new HashSet<>();
}

Thus, ORM automatically manages the many-to-many relationship through the intermediate table.