Foregin keys

Foreign keys in SQL are a type of constraint that is used to maintain referential integrity between two tables. A foreign key is a column or a set of columns in one table that uniquely identifies a row of another table. This relationship ensures that the value in the foreign key column corresponds to a valid value in the primary key column of the referenced table. By enforcing this constraint, SQL helps prevent actions that would destroy links between tables, such as deleting a row that is referenced by a foreign key in another table.

The primary purpose of foreign keys is to enforce referential integrity, which means that relationships between tables remain consistent. For example, if you have a customers table and an orders table, a foreign key in the orders table can reference the primary key in the customers table. This ensures that every order is associated with a valid customer. If a customer is deleted from the customers table, the database can be configured to automatically delete all related orders, set the foreign key to null, or prevent the deletion altogether, depending on the specified referential action.

Foreign keys also play a crucial role in database normalization, which is the process of organizing a database to reduce redundancy and improve data integrity. By using foreign keys, you can create a more modular database design where related data is stored in separate tables. This not only helps in maintaining data consistency but also makes the database more flexible and easier to manage. Proper use of foreign keys can significantly enhance the robustness and reliability of a database system.