Key Details Focus

SQL Primary Key Overview

A **Primary Key** in SQL is a constraint that uniquely identifies each record in a database table. As shown in the visual, the ID column is designated as the primary key, ensuring that each value in the column is both **unique** and **not null**. Primary keys prevent duplicate entries and are essential for data integrity. Only one primary key can be defined per table, though it can consist of single or multiple columns (known as a composite key). Moreover, primary keys are often used to create relationships between tables via foreign keys. Therefore, defining a proper primary key is foundational for designing reliable and relational database structures.

Key Features of SQL Primary Key

• Uniquely Identifies Records: Ensures no two rows have the same primary key value.
• Cannot Be NULL: Every primary key field must contain a value.
• Must Be Unique: Duplicate entries are not allowed in primary key columns.

What’s Included with SQL Primary Key

• Highlighted table example showing ID as the primary key for user records.
• Visual key symbol to reinforce its uniqueness and integrity enforcement.

How to Use SQL Primary Key

1. Define in CREATE TABLE: CREATE TABLE users (ID INT PRIMARY KEY, Name VARCHAR(50), City VARCHAR(50));
2. Use ALTER TABLE to add later: ALTER TABLE users ADD PRIMARY KEY (ID);

Ideal Uses and Placement

• Use primary keys for identifying user accounts, transactions, and system-generated records.
• Ideal for relational joins, indexing, and database normalization.

SQL Primary Key Specifications

• Data Requirement: NOT NULL and UNIQUE
• Structure: Can be single-column or multi-column (composite key)
• Relation: Referenced by FOREIGN KEY constraints

Explore More Resources

• Learn schema best practices: Products Page
• Explore SQL design tips: Our Blog
• Expand SQL knowledge: AI & QA Resources
• Reference guide: W3Schools Primary Key Documentation

Why Choose SQL Primary Key Guide?

Primary keys form the core of relational data integrity. Moreover, they are vital for table relationships and indexing. Therefore, every database designer must fully understand and apply them.

Design Better Databases Today!

Secure your data with confidence—define reliable primary keys for every SQL table!