oracle9i rownum 出现问题?

Question

/*
                      //这里开始处理分页显示
                      int allCos,allPage,getPage,tpage,bpage;
                      rSet=ment.executeQuery("select COUNT(ID) from 技术文章");
                      //if (rSet.next())
                          allCos=rSet.getInt("COUNT(ID)");  //获取总记录数
                      allPage=(allCos+6-1)/6;     //取得总页数
                      if (request.getParameter("pages")!=null)  //获取当前页
                          getPage= new Integer(request.getParameter("pages")).intValue();
                      else 
                          getPage=1;
                      tpage=(getPage-1)*6;  //取得开始记录
                      bpage=tpage+6;        //取得结束记录
                      */
                      int tpage=3,bpage=9;
                      String sql3="select * from 技术文章  where rownum>=tpage and rownum<=bpage";  \\出现异常
                      rSet=ment.executeQuery(sql3);
        
                      而在oracle9i的执行环境里执行
                      select * from 技术文章 where rownum>=2 
                      结果是未选定行 而数据库中有9条记录，这是为什么？