What types of relationships are on an ER diagram?

In ER diagrams (entity-relationship diagrams), the main types of relationships between entities are:

• One to one (1:1) — each record of one entity corresponds to exactly one record of the other entity.

• One to many (1:N) — one record of an entity can correspond to many records of another entity.

• Many to many (M:N) — a set of records of one entity corresponds to a set of records of another entity; usually implemented through an intermediate table.

These relationships reflect the rules and constraints in the modeled domain and help to properly organize the database structure.