ResultSet rs = stat.executeQuery(SQL);这是什么意思?
改为: ResultSet rs;Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
      con = DriverManager.getConnection("jdbc:odbc:aaa", "aaa", "aaa123");
      Statement stat = con.createStatement();      ResultSet rs;      //stat.close();
      if(rs.next()){
        pw.println("have~");
        rs=stat.executeQuery("SELECT COUNT(ID) AS cou FROM OrderSong");        if(rs.getInt("cou") >= 5){//只有rs.next()才能rs.getInt()
          pw.println("full");
        }else{
          pw.println("ok");
        }
      }      rs.close();
      con.close();