What is the difference between vbNullString, String.Empty and “”?

Question

All of these

• txtUsername.Text <> vbNullString
• txtUsername.Text <> String.Empty
• txtUsername.Text &

Answer 1

If are going to insert values to MS-SQL database and if column doesn't allows null(Not null) then strValue=vbNullString will generate exception but strValue="" will insert blank spaces.