SQL Server 2008 -- SPARSE Columns

• Sparse columns are ordinary columns that have an optimized storage for null values. Sparse columns reduce the space requirements for null values at the cost of more overhead to retrieve nonnull values. Consider using sparse columns when the space saved is at least 20 percent to 40 percent.

--**********SPARSE Columns********** USE [tempdb] GO --Declaring SPARSE columns CREATE TABLE SparseTest (ID       int IDENTITY(1,1),  LastName varchar(50) SPARSE NULL,  Salary   decimal(9,2) NULL) GO ALTER TABLE SparseTest  ALTER COLUMN Salary decimal(9,2) SPARSE GO

MSDN：http://technet.microsoft.com/en-us/library/cc280604.aspx