Glossary · Database

Foreign Key

A column in one table that references the primary key of another table, establishing a link between them.

A foreign key is a column or set of columns in a table that references the primary key of another table, creating a relationship between the two tables. Foreign keys enforce referential integrity–ensuring that a value in the foreign key column must exist in the referenced primary key column. This prevents orphaned records and maintains data consistency. Foreign key constraints can specify cascading actions: CASCADE (automatically delete/update related records), SET NULL (set foreign key to NULL), RESTRICT (prevent the operation), or NO ACTION. Understanding foreign key relationships is crucial for text-to-SQL systems to generate correct joins.

Fig — every answer ships with the tables, rows and SQL behind it.