Võõrvõtmed

Võõrvõtmed, meaning "foreign keys" in Estonian, are a fundamental concept in relational database design. They are a type of constraint that ensures referential integrity between two tables. A foreign key in one table points to a primary key in another table, establishing a link between the data in those tables. This link prevents actions that would destroy the relationship between the tables, such as deleting a record in the parent table if there are related records in the child table.

The table containing the foreign key is typically referred to as the child table or referencing table, while the table containing the primary key is called the parent table or referenced table. For example, in a database for an online store, a `customers` table might have a `customer_id` as its primary key. An `orders` table could then have a `customer_id` column as a foreign key, linking each order to the customer who placed it. This prevents an order from existing without a corresponding customer.

Implementing foreign keys is crucial for maintaining data consistency and accuracy. They help to prevent orphaned records, where a record in one table refers to a non-existent record in another. Databases enforce these constraints, ensuring that data operations comply with the defined relationships. This can involve defining actions for when a referenced primary key is updated or deleted, such as cascading the changes or preventing them altogether.