võõrvõtmesidest

Võõrvõtmesidest, often translated as "foreign key constraints" in English, are a fundamental concept in relational database management. They are rules that ensure referential integrity between two tables. A foreign key is a column or a set of columns in one table that refers to the primary key of another table. The primary key uniquely identifies each row in its table, while the foreign key establishes a link between rows in different tables.

The purpose of a võõrvõtmeside is to maintain consistency and accuracy of data across the database. When a võõrvõtmeside is defined, the database system enforces rules about what operations can be performed on the data. For instance, it prevents a record in the "child" table (the one with the foreign key) from referencing a non-existent record in the "parent" table (the one with the primary key). This means you cannot delete a record from the parent table if there are any corresponding records in the child table referencing it, unless specific cascading actions are defined. Similarly, you cannot insert a record into the child table with a foreign key value that does not exist as a primary key in the parent table.

These constraints are crucial for preventing data anomalies and ensuring that relationships between different pieces of information in a database remain valid and meaningful. They are a core mechanism for enforcing the relational model's principles.