Visual Basic® 2010 Unleashed

Introducing Nullable Types

As we mentioned talking about value types and reference types, value types have a default value that is typically zero whereas reference types have a default value that is Nothing. This is because a reference type can store null values, whereas value types cannot. Attempting to assign a null value to a value type would result in resetting to the default value for that type. This is a limitation, because there are situations in which you need to also store null values in value types, for example when fetching data from a SQL Server database. You can have a hypothetical Orders table where the Ship date column enables null values. SQL Server has its own data types, and one of these is the DBNull that enables null values. ...