Primaarvõtmele

Primaarvõtmele is a term used in database management systems to refer to a primary key. A primary key is a specific column or a set of columns within a database table that uniquely identifies each record or row. Its main purpose is to ensure data integrity and to provide a reliable way to access and reference individual records.

The primary key must contain unique values and cannot contain NULL values. This uniqueness constraint prevents duplicate entries for the same record, ensuring that each row is distinct. If a table has multiple columns that together form a unique identifier, this is referred to as a composite primary key. In many database systems, the primary key is also automatically indexed, which significantly speeds up data retrieval operations.

When designing a database, selecting an appropriate primary key is crucial. It should be stable, meaning its value should not change over time, and it should be as simple as possible to manage. Common choices for primary keys include unique identifiers like auto-incrementing integers (often called surrogate keys) or existing unique attributes like social security numbers (natural keys), although natural keys can sometimes be problematic due to potential changes or variability. The primary key serves as the main reference point for relationships between different tables in a relational database, forming the basis for foreign key constraints.