What are in SQL Server User Instances that make them impossible in non-Express Editions?
问题 After developing for a few years (or more), I still do not understand: What makes User Instances impossible/incompatible with Developer (or any other) edition of SQL Server? Why has developer to install more than one (i.e. developer edition) of SQL Server because user instances are available only through Express Edition? Update: @Damien_The_Unbeliever wrote in his answer, "User instances are pretty well expected to be standalone databases, only used by a single application, and meaningless