MySelect = @"SELECT ContenutoFile,NomeFile FROM tabAllegatiCommessa WHERE (IdAllegato = 37) ";

        DataSet dataSet = new DataSet();
        OleDbDataAdapter adapeter = new OleDbDataAdapter(MySelect, new OleDbConnection(connectionString));

        adapeter.Fill(dataSet);        

        foreach (DataRow item in dataSet.Tables[0].Rows)
        {
            byte[] dati = new byte[0];
            dati = (byte[])item[0];


            FileStream fs = new FileStream(@"G:\Siti Web\\" + item[1].ToString(), FileMode.Create, FileAccess.Write);

            fs.Write(dati, 0, dati.Length);
            fs.Close();

        }