The relationships between entities are usually: 1 to 1 (1: 1), 1 to many (1: m), and many to1(m:/kloc-0

For example, there are two simple entities, a company and employees, and their relationship is1:m. A company can have multiple employees.

For example, there are two entities, namely students and books, and their relationship is m: n, thus forming the middle table for students to borrow books. In this way, 1 can be borrowed by many people, and 1 can also borrow more books.