SQL PRIMARY KEY Constraint The PRIMARY KEY constraint is used to uniquely identify each record in a table. Primary keys must contain unique values, and cannot contain NULL values. …

Aug 5, 2019 · This article demonstrates how to add a primary key to an existing table in SQL Server using Transact-SQL. A primary key is a column that has been configured as the unique …

May 15, 2025 · Creating a primary key in an existing table requires ALTER permission on the table. In Object Explorer, right-click the table to which you want to add a unique constraint, and …

May 13, 2025 · Learn to add a primary key to existing SQL tables with ALTER TABLE in SQL Server, MySQL, PostgreSQL, and Oracle.

In this tutorial, you will learn how to use the SQL PRIMARY KEY constraint to add a primary key to the table.

Jun 28, 2024 · This tutorial covers SQL Primary Key definitions, rules, How to add a primary key to an existing table in SQL, interesting facts, and more with detailed examples.

Jul 23, 2025 · A primary key can be defined on a single column (simple primary key) or multiple columns (composite primary key). Creating a primary key automatically creates a unique index …

Sep 24, 2024 · These examples demonstrate how to add a primary key in SQL using auto-incrementing columns, streamlining the process of generating unique identifiers. FAQs About …

Here you will learn what is a primary key and how to create it in a new or existing table in the SQL Server database.

Mar 3, 2024 · First, when creating a table, you specify which column (s) will serve as the primary key. It’s possible to have a primary key made up of multiple columns, known as a composite …