Primary Key

What does Primary Key mean?

A Primary Key (PK) is a unique identifier assigned to each row in a database table. It enforces the entity integrity of a table by ensuring that no two rows have the same value for the primary key column(s). The primary key uniquely identifies each record in the table and maintains the relationship between tables in a Relational Database management system (RDBMS).

A PK column can be a single column or a composite of multiple columns. Composite primary keys are used when a single column is not sufficient to uniquely identify a row. For example, in a table of employee records, the combination of employee ID and date of birth could be used as a composite primary key, ensuring that each employee has a unique identifier within the table.

Applications

Primary Keys play a crucial role in database management and data integrity:

• Unique Identification: PKs ensure that each record in a table is uniquely identified, allowing for efficient data retrieval and manipulation.
• Data Integrity: By enforcing uniqueness, PKs prevent duplicate rows from being inserted into a table, maintaining data Consistency and reliability.
• Referential Integrity: PKs are used to establish relationships between tables through foreign keys. This allows for data to be linked and referenced across multiple tables, ensuring data integrity and consistency.
• Indexing: PKs are often used as the basis for indexes, which speed up data retrieval by allowing the database to quickly locate specific records based on their primary key values.
• Data Manipulation: PKs simplify data manipulation tasks such as updates, deletions, and inserts by providing a unique reference for each row.

History

The concept of a Primary Key has its roots in the early days of database management. In the 1970s, the relational database model, developed by E.F. Codd, introduced the concept of primary keys as a fundamental Component of relational database design.

The SQL (Structured Query Language) standard, developed in the 1980s, formalized the use of primary keys in database management systems. SQL introduced the PRIMARY KEY constraint, allowing database administrators to explicitly define which column or columns should serve as the primary key for a table.

Over the years, primary keys have become an indispensable feature of relational database management systems, providing the foundation for data integrity, efficient data retrieval, and reliable data manipulation.