oracle 报未明确定义列

报这个错误的原因在于选出的结果集中包含相同的字段，数据库不知道应该以哪个字段为准。

      select U.*
  from (select q.jslongitude_gps as **gpslatitude**,q.jslatitude_gps as **gpslatitude**,q.jslongitude_amap as lontitude,q.jslatitude_amap as latitude, ROWNUM RN
          from qcres q
         where q.jslongitude_gps is null
            and q.jslatitude_gps is null
            and q.jslongitude_amap is not null
            and  q.jslatitude_amap is not null) U
 where RN <![CDATA[<=]]>40

如上出现了两个相同的gpslatitude ，那么数据库就无法获知应该获取哪个字段。