Võõrvõtmeside

Võõrvõtmeside, which translates to "foreign key relationship" in English, is a fundamental concept in relational database management. It establishes a link between two tables, ensuring data integrity and consistency. Essentially, a foreign key in one table refers to the primary key of another table.

The table containing the foreign key is called the referencing table or child table, while the table containing the primary key is known as the referenced table or parent table. This relationship dictates that any value entered into the foreign key column must already exist in the primary key column of the referenced table, or be null if the foreign key constraint allows it.

For example, in a database for an online store, an "orders" table might have a "customer_id" column. This "customer_id" would be a foreign key referencing the "customer_id" primary key in a "customers" table. This ensures that every order is associated with a valid customer.

Foreign key constraints prevent "orphan records," meaning you cannot have an order without a corresponding customer. They also define how relationships are maintained when data is updated or deleted. For instance, a foreign key constraint can be set to cascade deletions, so deleting a customer record automatically deletes all their associated orders, or it can prevent deletion if related records exist.

Implementing foreign key relationships is crucial for maintaining the accuracy and reliability of data within a relational database. They enforce business rules and simplify data retrieval by allowing developers to query related information across different tables.