Q:

Updating Database using Visual Basic 2010

I ask here because I'm having a problem with my code.
It's suppose to update an SQL Database but instead it shows an error which is

Key cannot be null. Parameter name: key

It highlights the SQLConnection.Open()
 Private Sub btnTakeQuiz_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnTakeQuiz.Click
        Dim SQLStatement As String = "UPDATE class SET exam=Yes WHERE name = " & Session("name") & ""
        TakeQuiz(SQLStatement)
End Sub

Public Sub TakeQuiz(ByRef SQLStatement As String)
    Dim cmd As MySqlCommand = New MySqlCommand
    SQLConnection.Open()
    With cmd
        .CommandText = SQLStatement
        .CommandType = CommandType.Text
        .Connection = SQLConnection
        .ExecuteNonQuery()
    End With
    SQLConnection.Close()
    SQLConnection.Dispose()
    Server.Transfer("Quiz.aspx", True)
End Sub

Session("name") Contains the current login user name.
Class is my table.
exam is a column if it's yes then it means the user has took an exam.
What I'm trying to do is to limit a user to one quiz only. Can anyone help me?

A:

The "Yes" and session value will be treated as a column or data source which will give a query like this.
UPDATE class SET exam=Yes WHERE name = <SessionValue>

Can you try this?
Dim SQLStatement As String = "UPDATE class SET exam='Yes' WHERE name = '" & Session("name") & "'"

