How to Establish Unique Constraints in SQL Server 2005?

Enforcing Unique Constraints in SQL Server 2005 Databases

This guide demonstrates how to define unique constraints in SQL Server 2005, guaranteeing unique values within a specified table column. We'll cover two primary methods: using T-SQL and employing the database diagram interface.

Method 1: T-SQL Approach

1. Construct the following T-SQL statement:

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

2. Replace the placeholders:

   • <tablename></tablename>: The name of your target table.
   • <constraintname></constraintname>: A descriptive name for the unique constraint.
   • <columnname></columnname>: The column to enforce uniqueness upon.

Example:

ALTER TABLE Orders ADD CONSTRAINT UK_OrderNumber UNIQUE NONCLUSTERED (OrderNumber)

This command adds a non-clustered unique index named UK_OrderNumber to the Orders table, ensuring that the OrderNumber column contains only unique values.

Method 2: Database Diagram Interface

1. Right-click the table in your database diagram.
2. Select "Indexes/Keys" from the context menu.
3. Click "Add" to create a new index.
4. In the "Columns" tab, select the column(s) requiring unique values.
5. Set "Is Unique" to "Yes".
6. In the "General" tab, provide a meaningful index name (e.g., IX_OrderNumber_Unique).

By applying either method, you effectively maintain data integrity and uniqueness within your SQL Server 2005 database. This prevents duplicate entries and ensures data accuracy.

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