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3 Examples of a Foreign Key

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A foreign key is a field or set of fields that are used to establish relationships between rows in a database.

Example (1)

A customer table contains a row for each customer. Each customer row has a foreign key called ADDRESS_ID that points to the customer's address.

Example (2)

A star table contains a row for each known star. Each star row has a foreign key called GALAXY_ID that points to the star's Galaxy.

Example (3)

An actor table contains a row for each actor in a movie database. Each actor row has a foreign key called FAVORITE_ACTOR that points to the id of the Actor's favorite Actor.

Technical Overview

A foreign key is a type of constraint that can be defined for a database. When defined, it helps the database to enforce referential integrity between tables. A foreign key must be defined as a primary key in the parent table. A table can contain a foreign key to itself. A foreign key must exist in the parent table or be null.

Parent & Child

A table with a foreign key is often referred to as a child with the related table being called a parent. The parent/child terminology is a little misleading as the relationship between tables isn't necessarily a hierarchy.

Recursive Foreign Key

A foreign key in a table that refers to itself is known as a recursive foreign key.
Overview: Foreign Key
Definition (1)
A field or set of fields that are used to establish relationships between rows in a database.
Definition (2)
A constraint that indicates a column or set of columns in a table is a reference to the primary key of another table or a self-reference to the table's own primary key.
Establishing relationships between data entities.
Enforcing referential integrity in a database.
Applies to
Relational Databases
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