Databases Beginner

What is Foreign Key?

A column that creates a link between two tables by referencing the primary key of another table.

Foreign keys enforce referential integrity — ensuring relationships between tables remain consistent. For example, an orders table might have a customer_id foreign key referencing the customers table.

Foreign key constraints can specify behavior on delete/update: CASCADE (propagate changes), SET NULL, SET DEFAULT, or RESTRICT (prevent action). They are fundamental to relational database design.

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Rules enforced by the database to maintain data integrity, including NOT NULL, UNIQUE, CHECK, PRIMARY KEY, and FOREIGN KEY.

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