Primaarvõtmed

Primaarvõtmed, or primary keys, are fundamental concepts in relational database design. A primary key is a column or a set of columns in a table that uniquely identifies each row. This means that no two rows in the table can have the same value or combination of values in the primary key column(s). The primary key is essential for maintaining data integrity and ensuring that each record can be unambiguously accessed and referenced.

The establishment of a primary key serves several crucial purposes. Firstly, it guarantees entity integrity, preventing duplicate records and ensuring that each row is distinct. Secondly, it provides a mechanism for establishing relationships between different tables in a database through foreign keys. A foreign key in one table references the primary key of another table, creating a link that allows for data to be joined and queried across multiple tables.

Primary keys are typically chosen to be a single column with a unique identifier, such as an auto-incrementing integer (e.g., `CustomerID`, `OrderID`). However, composite primary keys, which consist of two or more columns, are also used when a single column cannot guarantee uniqueness. The columns chosen for a primary key should be immutable, meaning their values should not change once assigned. Databases enforce primary key constraints automatically, preventing the insertion of duplicate values or NULL values into the primary key column(s). Understanding and properly implementing primary keys is a cornerstone of effective database management.