SemanticException [错误10004]：行11:18无效的表别名或列引用

Question

这个问题与my previous question的答案有关。请注意datetime是字符串。因此我将其转换为unix时间戳。

我在Hive 1.2.1中执行此查询：

select count(*) / count(distinct to_date(datetime)) as trips_per_day 

from (select radar_id,to_unix_timestamp(datetime),lead(radar_id) over w as 
      next_radar_id,lead(to_unix_timestamp(datetime)) over w as 
      next_datetime 
      from mytable 
      where radar_id in ('A21','B15') window w as 
     (partition by car_id order by to_unix_timestamp(datetime))) t 

where radar_id = 'A21' and next_radar_id = 'B15' 
      and to_unix_timestamp(datetime) + 30*60 > to_unix_timestamp(next_datetime);

但是我收到以下错误：

  

SemanticException [错误10004]：行11:18无效的表别名或   列引用＆＃39; datetime＆＃39; :(可能的列名是：radar_id，_c1，   next_radar_id，next_datetime）

哪里出错？