What is the role of a primary key in a database table and why is it necessary?

A Primary Key is a unique identifier for each record in a database table. Its roles and necessity:

• Uniqueness: ensures that each row in the table is different from others.
• Identification: allows unambiguous reference to a specific record.
• Query optimization: primary keys are usually indexed, which speeds up search and table joins.
• Relationships between tables: used to create foreign keys, ensuring data integrity.

For example, in a users table, the id field can be a primary key to uniquely identify each user.