Databases: Understanding Primary Keys

In database design, a primary key is a crucial concept. It's a special column (or set of columns) in a table that uniquely identifies each record (row) within that table.

Purpose of a Primary Key

The primary key serves several important purposes:

• Uniqueness: It guarantees that no two records in the table have the same primary key value.
• Identification: It provides a reliable way to identify and retrieve specific records.
• Relationship Building: Primary keys are often used to establish relationships between different tables in a database.

Identifying a Primary Key

A good primary key should meet the following criteria:

• Unique: Each value must be distinct.
• Not Null: The primary key column(s) cannot contain empty or missing values.
• Immutable: The value should not change over time.

Example Table

Consider a table called Students. This table stores information about students in a school.

Student ID	First Name	Last Name	Grade
101	Alice	Smith	10
102	Bob	Johnson	11
103	Charlie	Brown	10

In this Students table, the Student ID is a suitable primary key. It fulfills all the criteria for a primary key: it is unique, not null, and should ideally not change.

Key Takeaway

Understanding primary keys is fundamental to database design. They ensure data integrity and allow for efficient data management.