Software → Databases
Foreign Key
A relational constraint where values in one table refer to primary keys in another table.
Motivation
A foreign key solves the problem of keeping relationships between tables valid.
Where it fits
It belongs to relational databases and data modeling.
Mental model
A foreign key says: this value must refer to an existing row somewhere else.
Important details
Foreign keys help enforce referential integrity and make domain relationships explicit in the database.
Common mistakes
- Skipping foreign keys because the application “should handle it”.
- Confusing joins with foreign key constraints.