The proper way to implement unique constraint that allows multiple NULL values in SQL Server

Question

I need 1 column in the table to hold unique non-null values or NULL. TSQL UNIQUE constraint treats 2 NULLs as equal, so I cannot

Answer 1

SQL 2008 allows you to define a filtered index - essentially an index with a WHERE clause - see Phil Haselden's asnwer to this question for MSDN links and an example.