Description: A primary key is a unique identifier for a record in a database table, ensuring that no two records have the same key.
History: The concept of a primary key was formalized with the development of relational databases in the 1970s, particularly with the relational model proposed by Edgar F. Codd in 1970. Codd introduced the idea that data should be organized in tables and that each table should have a unique key to identify its records. As relational databases became popular in the 1980s and 1990s, the implementation of primary keys became a standard practice in database design.
Uses: Primary keys are used in relational databases to ensure the uniqueness of records and facilitate referential integrity. They are essential for establishing relationships between tables, allowing one table to reference another through foreign keys. Additionally, primary keys improve efficiency in queries and search operations, as indexes can be created on them to speed up data access.
Examples: An example of a primary key is an employee identification number in an employee table, where each employee has a unique number that identifies them. Another example could be the ISBN of a book in a books table, where each book has a distinct ISBN that differentiates it from others.
