What's the proper method of adding a unique constraint to an existing table? When I add the new column, and attempt to create a unique key, I receive the following:
The CREATE UNIQUE INDEX statement terminated because a duplicate key was found for the object name 'dbo.table' and the index name 'Indexname_uq'. The duplicate key value is (<NULL>).
and I understand why I'm getting that, but what's the correct way of handling this situation? Essentially, I just want to create a unique key/index so that when I'm importing rows of data into a table it'll throw an error if the record already exists.