What is a one-to-one relationship in data modeling? How do you implement this relationship in a database? The examples in this article will answer these questions. There are three types of relationships between entities (tables) in data modeling: One-to-many relationships (also denoted as 1:M). Many-to-many relationships (M:N). One-to-one relationships (1:1). The most common type of relationship is a one-to-many relationship, where a record in one entity can be referenced by multiple records in another entity.