How Can I Create Unique Constraints in SQL Server 2005?

Enforcing Data Uniqueness in SQL Server 2005 Tables

Maintaining data integrity is crucial, and a key aspect is ensuring uniqueness within specific columns or column combinations. SQL Server 2005 provides unique constraints to achieve this, preventing duplicate entries. Let's explore two approaches:

Method 1: Using Transact-SQL (T-SQL)

The T-SQL approach offers direct control through scripting. Here's the syntax:

ALTER TABLE <tablename> ADD CONSTRAINT <constraintname> UNIQUE NONCLUSTERED (<columnname>)

Replace <tablename></tablename>, <constraintname></constraintname>, and <columnname></columnname> with your table's name, the desired constraint name, and the column(s) you want to make unique, respectively. UNIQUE NONCLUSTERED specifies a non-clustered unique index.

Method 2: Utilizing the Database Diagram

A visual method is available through the SQL Server Management Studio database diagram:

1. Right-click the target table and select "Indexes/Keys."
2. Click "Add" to initiate index creation.
3. In the Properties window:
   • Choose the column(s) requiring uniqueness.
   • Set "Is Unique" to "Yes."
   • Provide a descriptive constraint name.

This graphical approach simplifies constraint creation, particularly for users comfortable with visual tools. Both methods achieve the same result: guaranteeing data uniqueness and enhancing database integrity.

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