set up unique column in another column besides primary key

[adonet]

Is it possible to set up unique column in another column besides primary key? How to do it?

 

[cooperman1275]

Use Enterprise Manager to Design the table.
Create the new column.
Select the newly created column, right click, Indexes/Keys.
Create a new index on the column name, and make sure to check "Create Unique" before saving amended design.
Any attempt to insert a non-unique value into the new column will result in a Violation of Unique Key Constraint error.
Is this what you wanted to do?

 

[adonet]

Thank you. It is what I want. It is better to setup in SQL server for unique or use code to violate user's input? That is, as I did before, I used code to check user's input with SQL server to find out if input is unique or not.