A foreign key is a relationship between two entities. Generally speaking, inter-entity relationships are one-to-many, e.g., an ORDER has many ORDER LINEs, and so forth. Even a case that may start out ...

Occasionally one sees an entity-relationship diagram (ERD) having an unusual characteristic. The unusual element is an entity (or more than one) that seems to have a relationship with every other ...

Databases are used in many different settings, for different purposes. For example, libraries use databases to keep track of which books are available and which are out on loan. Schools may use ...