Sep 25, 2010 · Although both a UNIQUE constraint and a PRIMARY KEY constraint enforce uniqueness, use a UNIQUE constraint instead of a PRIMARY KEY constraint when you want …

Nov 22, 2024 · This topic describes how to create a unique index on a table in SQL Server by using SQL Server Management Studio or Transact-SQL. A unique index guarantees that the …

The UNIQUE constraint ensures that all values in a column are different. Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns.

Aug 27, 2021 · Unique Constraint or Unique key in SQL Server enforces the uniqueness of the column value. i.e. no two rows of a table can have the same values. In this tutorial, we will …

It is recommended to use Unique constraint instead of Primary key constraint whenever you want to enforce uniqueness in a column. Unlike Primary key constraint, Unique constraints allow …

Oct 7, 2022 · Though the PRIMARY KEY consists of UNIQUENESS and NOT NULL, only one PRIMARY KEY constraint is allowed for each table. If the table contains additional columns …

To assign a particular name to a UNIQUE constraint, you use the CONSTRAINT keyword as follows: person_id INT IDENTITY PRIMARY KEY, first_name VARCHAR (255) NOT NULL, …

The UNIQUE key constraint in SQL Server ensures that all values in a column or a combination of columns are distinct. It is used to prevent duplicate values in specified columns while allowing …

What is a unique constraint in SQL Server? A unique constraint is a single field or combination of fields that uniquely defines a record. Some of the fields can contain null values as long as the …

Mar 17, 2025 · It explains how to use the SQL Server unique key to guarantee that the data in a column or group of columns is unique. In addition, how unique is different from the primary key.