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 …

Feb 6, 2026 · The PRIMARY KEY constraint in SQL uniquely identifies each record in a table and ensures strong data integrity. It prevents duplicate and NULL values, making it essential for reliable …

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

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 …

Oct 22, 2020 · Question: What is a SQL Primary Key? In SQL databases, a primary key is a unique identifier for each table row; it does not allow duplicate or NULL values and guarantees the …

Aug 6, 2025 · A primary key is a column in a database table that uniquely identifies each row. That means no two rows can have the same value in this column, and it can’t be left empty.

Aug 7, 2025 · Understand what an SQL primary key is and its function in database relationships and query performance in this technical tutorial.

In the relational model of databases, a primary key is a designated set of attributes (column (s)) that can reliably identify and distinguish between each individual record in a table.

In SQL Server, a Primary key is a constraint that uniquely identify each row in the table. It enforce data integrity in tables. A table can have only one primary key. A primary key can be defined on one …

Master SQL primary keys with syntax, examples, and best practices. Learn how to create, use, and optimize keys for performance, integrity, and relationships.