See Also: DBNull Members
When a SQL query returns null, it is converted to a System.DBNull value, specifically the DBNull.Value instance, which is the only instance of the type ever used. Thus, one may compare values t DBNull using reference equality to DBNull.Value (== DBNull.Value). You then do not need to create a new instance of this type.
You can convert this to a blank string by using Convert.ToString(). See example below.
C# Example
SqlConnection dbConn = new SqlConnection("server=myserver;database=mydb;uid=myuserid;pwd=mypassword");
dbConn.Open();
SqlCommand command = new SqlCommand("select something that returns a null value", dbConn);
SqlDataReader reader = command.ExecuteReader();
while (reader.Read()) {
// if it's a DBNull, myString will contain a blank String
string myString = Convert.ToString(reader.GetValue(0));
// if you prefer to check for the DBNull try this
object possibleNull = reader.GetValue(0);
if (possibleNull == DBNull.Value) {
// do something
}
}
reader.Close();
dbConn.Close();