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 and column sets are defined by using the CREATE TABLE or ALTER TABLE statements.
A sparse column cannot be part of a clustered index or a unique primary key index.
http://blogs.technet.com/b/andrew/archive/2008/02/28/sql-server-2008-sparse-columns.aspx
http://msdn.microsoft.com/en-us/library/cc280604.aspx
SQL Server 2008 Editions & Difference
- Enterprise Edition
- Standard Edition
- Workgroup Edition
- Web Edition
- Compact Edition
It supports a subset of the standard data types, does not support stored procedures or Views or multiple-statement batches (among other limitations). It is limited to 4 GB maximum database size and cannot be run as a Windows service, Compact Edition must be hosted by the application using it. The 3.5 version includes considerable work that supports ADO.NET Synchronization Services - Express Edition
- SQL Server 2008 Express Edition.
- SQL Server 2008 Express with Tools.
- SQL Server 2008 Express with Advanced Tools.
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