Tietokantaavain

Tietokantaavain, known in English as a database key, is a fundamental concept in relational database management systems. It is a column or a set of columns within a table whose values uniquely identify each row. This uniqueness is crucial for maintaining data integrity and establishing relationships between different tables.

There are several types of database keys. A primary key is a specific type of key that is chosen as the main identifier for a table. It must contain unique values and cannot contain null values. A foreign key, on the other hand, is a column or a set of columns in one table that refers to the primary key in another table. This mechanism is used to link tables together, creating a relational structure. Unique keys also enforce uniqueness on a column or set of columns but allow for null values. Candidate keys are any columns or sets of columns that could potentially serve as a primary key, meaning they are unique and not null.

The use of keys ensures that each record in a database can be accessed and distinguished unambiguously. They prevent duplicate records and help in organizing and querying data efficiently. For instance, when retrieving information from multiple related tables, foreign keys are used to join the tables and combine the relevant data. The integrity of the database relies heavily on the correct implementation and enforcement of these key constraints.