How to ensure non-null duplicate values are not inserted in SQL Server 2005
<p>I have a history database in <code>SQL Server 2005</code> that is used to archive data from live database. I need to add a column in history database named RowID INT. This column cannot be made as identity since it need to store values from live database. </p>

<p>Note: In the live database the RowID is identity column. This column was added by me in live database also recently.</p>

<p>I need to make sure that in history database, the non-null values inserted into this column is unique. I understand that in SQL Server, we cannot make a nullable column as unique.</p>

<p>So, in SQL Server 2005, what is the most efficient way to make sure that insertion of <code>non-null duplicate values</code> into RowID columns throws an error?</p>