public DataTable QueryDataTable(string sql)
        {
            DataTable dt = new DataTable();
            using (
            OdbcConnection dbconn = new OdbcConnection(ConfigurationManager.ConnectionStrings["ODBCConnectionString"].ConnectionString))
            {
                OdbcDataAdapter DataAdapter = new OdbcDataAdapter(sql, dbconn);
                DataAdapter.Fill(dt);
            }
            return dt;
        }

//连接串错了

//for access
cn= new OdbcConnection("Driver={Microsoft Access Driver (*.mdb)};
DBQ=D:\\Program Files\\Microsoft Office\\Office10\\Samples\\Northwind.mdb;UID=;PWD=;");
   
//for SQL server
cn= new OdbcConnection("Driver={SQL Server};Server=mySQLServer;UID=sa;
PWD=myPassword;Database=Northwind;");


//for Oracle
cn= new OdbcConnection("Driver={Microsoft ODBC for Oracle};Server=myOracleServer;
UID=demo;PWD=demo;");

//for dsn
cn= new OdbcConnection("dsn=myDSN;UID=myUid;PWD=myPwd;");