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 …

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

Jul 23, 2025 · The PRIMARY KEY constraint in SQL is one of the most important constraints used to ensure data integrity in a database table. A primary key uniquely identifies each record in a 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 …

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. It’s the most …

What is a primary key? A primary key is a column or columns in a database table with values that uniquely identify each row or record. For example, an employee ID column could be a primary key in …

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

What Is a Primary Key in SQL? A primary key in SQL is a column or set of columns whose values uniquely identify every row in a table. The database engine enforces two key rules on this column: …

Here, the college_id column is the PRIMARY KEY. This means that the values of this column must be unique and it cannot contain NULL values. Note that the above code works in all major database …

Following are some of the important properties of SQL PRIMARY KEY: It contains only a unique value. It can not be null. One table can have only one Primary Key. A primary key length cannot be more than …