idegenkulcsokkal

Idegenkulcsokkal is a Hungarian term that translates to "foreign keys" in English. In the context of relational databases, a foreign key is a column or a set of columns in one table that refers to the primary key of another table. Its purpose is to establish and enforce a link between two tables, ensuring referential integrity.

When a foreign key constraint is defined, it specifies that the values in the foreign key columns must match values in the referenced primary key columns, or they must be null. This prevents orphaned records, meaning a record in the "child" table (the one with the foreign key) cannot exist without a corresponding record in the "parent" table (the one with the primary key). For example, if a "Customers" table has a primary key "CustomerID" and an "Orders" table has a "CustomerID" as a foreign key referencing the "Customers" table, it ensures that every order is associated with an existing customer.

The implementation of foreign keys can involve various actions when the referenced primary key is updated or deleted. These actions, often referred to as referential actions, include CASCADE (automatically update or delete related records), SET NULL (set the foreign key to null), or RESTRICT (prevent the update or deletion if related records exist). Proper use of foreign keys is crucial for maintaining data consistency, accuracy, and the overall integrity of a relational database.