SQL 2008: How to make a column Unique

Add a unique constraint for that column:

alter table Foo add constraint UQ_Name unique (Name)

To add it through SQL Management Studio UI:

1. Open SQL Server Management Studio.
2. Expand the Tables folder of the database where you wish to create the constraint.
3. Right-click the table where you wish to add the constraint and click Design.
4. In Table Designer, click Indexes/Keys.
5. Click Add.
6. Choose Unique Key in the Type drop-down list.