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

4 ways:

• Filtered index (SQL Server 2008) <- recommended based on your tags
• Trigger (mentioned)
• Indexed view (in your question)
• Unique constraint/index with computed column (in your question)