Primary Key in DBMS

In Database Management Systems (DBMS), a primary key is a unique identifier for each record in a database table. It ensures that each row in the table can be uniquely identified. A primary key is critical for data integrity and efficient data retrieval. Here’s what defines a primary key:

• Uniqueness: The values in a primary key column must be unique across all rows in the table. No two rows can have the same value in the primary key field.
• Non-nullability: Every record must have a value for the primary key. It cannot contain NULL values, ensuring that each record can be uniquely identified.
• Single or Composite Key: A primary key can consist of one column (a single primary key) or multiple columns (a composite primary key) if a single column is not sufficient to uniquely identify a record.
• Indexing: The DBMS automatically creates an index on the primary key column(s) to speed up data retrieval operations.
• Relationships: It is used to define relationships with other tables through foreign keys.

Example:

Suppose you have a table Students:

In this table, StudentID could be the primary key because it uniquely identifies each student and cannot be null.

How to Choose a Primary Key?

When designing a database, selecting the right primary key from all possible candidate key is crucial:

• Uniqueness: The key must uniquely identify each record.
• Stability: The value of the primary key should not change frequently.
• Simplicity: Ideally, choose a primary key that is simple and straightforward.
• Efficiency: Consider the size and type of the data when choosing a primary key for optimal performance.