How to pass a querystring variable to be used in an sql query?

 I just cant seem to get this work! What am I doing wrong here?
 
  protected void Page_Load(object sender, EventArgs e)
    {
        string query = Request.QueryString["Id"];
        ;
        
        string SQL = "SELECT title FROM mb_messages WHERE mb_id ='"+ query +"'";
        


        OleDbConnection myConn = new OleDbConnection("Provider=Microsoft.Jet.OleDb.4.0; Data Source=|DataDirectory|mbbase.mdb");
        OleDbCommand cmd = new OleDbCommand(SQL, myConn);
        
        myConn.Open();
   &n ...