如何连接来自不同位置的SQLite数据库?

我试着加入来自不同地方的SQLite数据库;

folder1=我的主数据库所在的位置。

folder2=在我的本地C。

internal void Fill_DataCollection(string folder2)
    {
        string SQL = "ATTACH '" + folder2 + "' AS db2";
        SQLiteCommand cmd = new SQLiteCommand(SQL);  

        string connectionString = string.Format("Data Source={0}", folder1 .databasePath);

        using (var conn = new SQLiteConnection(connectionString))
        {
            conn.Open();
            cmd.Connection = conn;
            cmd.CommandText = string.Format("SELECT * FROM tblMain A inner join db2.tblSub B on B.ID = A.ID");

            var _dataAdapter = new SQLiteDataAdapter(cmd.CommandText, cmd.Connection);

            DataSet _dataSet = new DataSet();
            DataTable _dataTable = new DataTable();

            _dataSet.Reset();
            _dataAdapter.Fill(_dataSet);

            _dataTable = _dataSet.Tables[0];
            var rows = _dataTable.Rows; ;

            foreach (DataRow row in rows)
            {
                var reportID = row.ItemArray[1];
                string status = row.ItemArray[3] as string;
                string vendorStatus = row.ItemArray[3] as string;

                var TechdataProperties = new TechdataProperties
                {
                    ReportID = reportID.ToString(),
                    Status = status,
                    VendorStatus = vendorStatus,

                };
                _techdataCollection.Add(TechdataProperties);
            }

            conn.Close();
        }
    }

此代码出错:

SQLite错误(1):没有这样的表:db2.tblSub