How to create a unique index on a NULL column?

sql sql-server indexing constraints unique
Nuno G picture Nuno G · Oct 10, 2008 · Viewed 99.6k times · Source

I am using SQL Server 2005. I want to constrain the values in a column to be unique, while allowing NULLS.

My current solution involves a unique index on a view like so:

CREATE VIEW vw_unq WITH SCHEMABINDING AS
    SELECT Column1
      FROM MyTable
     WHERE Column1 IS NOT NULL

CREATE UNIQUE CLUSTERED INDEX unq_idx ON vw_unq (Column1)

Any better ideas?

Answer

Phil Haselden picture Phil Haselden · Jul 7, 2010

Using SQL Server 2008, you can create a filtered index: http://msdn.microsoft.com/en-us/library/cc280372.aspx. (I see Simon added this as a comment, but thought it deserved its own answer as the comment is easily missed.)

Another option is a trigger to check uniqueness, but this could affect performance.

Related questions

Creating an index on a table variable

Can you create an index on a table variable in SQL Server 2000? i.e. DECLARE @TEMPTABLE TABLE ( [ID] [int] NOT NULL PRIMARY KEY ,[Name] [nvarchar] (255) COLLATE DATABASE_DEFAULT NULL ) Can I create an index on Name?

Read More
Rebuild all indexes in a Database

I have a very large SQL Server 2008 R2 database (1.5TB) and will be copying some data from column to column within the same table. I've been told that the schema has a large number of indexes and was wondering if …

Read More
sql primary key and index

Say I have an ID row (int) in a database set as the primary key. If I query off the ID often do I also need to index it? Or does it being a primary key mean it's already indexed? …

Read More