public string mdb_exe_return(string sql)
 {
     data_conn cn = new data_conn();
     OleDbConnection connection1 = cn.mdb_conn();
     OleDbCommand command1;
     connection1.Open();
     OleDbDataAdapter da = new OleDbDataAdapter();
     DataSet ds = new DataSet();
     command1 = new OleDbCommand(sql, connection1);
     command1.ExecuteNonQuery();
     command1 = new OleDbCommand("select @@identity", connection1);
     da.SelectCommand = command1;
     da.Fill(ds, "aa");
     connection1.Close();
     return ds.Tables["aa"].Rows[0][0].ToString();
 }