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. Each table …

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 identifier for …

The table already has an existing compound-key [PersonId, Pname] as the primary key. Now I want to modify that existing compound-key to have one more field [PMid].

Nov 18, 2025 · You can define a primary key in the SQL Server Database Engine by using SQL Server Management Studio or Transact-SQL. Creating a primary key automatically creates a corresponding …

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

Dec 12, 2025 · This tutorial guides you through the complete process of adding a primary key to an existing table using T-SQL and SQL Server Management Studio (SSMS), tailored for a professional …

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 · How to Add Primary Key to Existing Table in SQL? Now we will see how to add Primary Key to existing table in SQL: You can use the ALTER statement to create a primary key. However, …

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 on the key …

Primary Key can be created in two ways in SQL Server: A primary key can be configured in the create table T-SQL script. Append CONSTRAINT statement at the end of all column declaration. The name …