What is a primary key?

A primary key is a field or combination of fields in a database table that uniquely identifies each record in the table. It is a fundamental concept in database design and is used to ensure the integrity and consistency of data in the table.

A primary key is a special type of constraint that ensures that no two records in the table have the same values in the primary key field or fields. It also ensures that each record in the table has a unique identifier, which can be used to join related tables and perform other operations on the data.

In most database management systems (DBMS), the primary key is used as the primary means of accessing and manipulating the data in a table. It is often used to enforce referential integrity constraints, which help ensure that the relationships between tables are consistent and reliable.

Common examples of primary keys include unique identifiers such as social security numbers, email addresses, and customer IDs. In some cases, a composite key made up of two or more fields may be used as the primary key to ensure uniqueness.