MS SQL Server - make column values unique

In this article, we would like to show you how to make column values unique in MS SQL Server.

Quick solution:

ALTER TABLE [table_name] 
ADD UNIQUE ([column_name]);

or

ALTER TABLE [table_name]
ADD CONSTRAINT [constraing_name] UNIQUE ([column1], [column2], [columnN]);

Practical example

To show how to make column values unique, we will use the following table:

Example 1 - make single column unique

In this example, we will make name column unique.

Query:

ALTER TABLE [users]
ADD CONSTRAINT [UC_username] UNIQUE ([name]);

Result:

Using query

SHOW INDEXES FROM [users];

Using HeidiSQL

Example 2 - make multiple columns unique

In this example, we will make name and country columns unique.

Query:

ALTER TABLE [users]
ADD CONSTRAINT [UC_user] UNIQUE ([name], [country]);

Result:

Using query

SHOW INDEXES FROM [users];

Using HeidiSQL: