Windows Small Business Server 2008 Premium includes SQL 2008 Standard Edition for Small Business. This version is feature by feature the same as SQL 2008 Standard with the difference that it must be installed in an Small Business Server domain or, if purchased separately, an environment with certain characteristics. But, what does that mean? SQL 2008 Standard for Small Business is supported for installation in a small business domain, which includes installing on one of the following Windows Server 2008 editions. Read the following documentation for installation and downgrade rights in Small Business Server 2008: Using SQL Server in Windows Small Business Server 2008 Premium Edition.
Source:→ SBS Blog