我在hadoop中有一个表，其中有不同传感器单元的采样时间数据 ts 1毫秒。我可以使用impala中的以下查询，使用不同聚合函数的组合对单个单元的数据进行重采样（假设我想使用 LAST_VALUE() 作为聚合函数）：

SELECT DISTINCT * 
from ( select ts_resample, unit,
last_value(Val1) over (partition by ts_resample order by ts rows between unbounded preceding and unbounded following) as Val1, 
last_value(Val2) over (partition by ts_resample order by ts rows between unbounded preceding and unbounded following) as Val2
from (
SELECT cast(cast(unix_timestamp(cast(ts/1000 as TIMESTAMP))/300 as bigint)*300 as TIMESTAMP) as ts_resample, 
ts as ts, unit as unit, Val1 as Val1, Val2 as Val2
FROM Sensor_Data.Table1 WHERE unit='Unit1') as t) as tt

如果我为一个单元运行这个查询，那么我得到的是正确的asnwer，没有问题。
但是如果我想根据一些聚合函数对每个单元的数据进行重采样，例如。 LAST_VALUE() 然后我得到了错误的答案和重采样结果为每个单位是相同的，虽然我有不同的数据为每个单位。下面给出了我正在运行的查询，我没有在其中指定任何单位 WHERE 条款：

SELECT DISTINCT * 
from(
select ts_resample, unit,
last_value(Val1) over (partition by ts_resample order by ts rows between unbounded preceding and unbounded following) as Val1, 
last_value(Val2) over (partition by ts_resample order by ts rows between unbounded preceding and unbounded following) as Val2
from (
SELECT cast(cast(unix_timestamp(cast(ts/1000 as TIMESTAMP))/300 as bigint)*300 as TIMESTAMP) as ts_resample, 
ts as ts, unit as unit, Val1 as Val1, Val2 as Val2
FROM Sensor_Data.Table1) as t) as tt

使用上述查询数据中现有三个单位得到的结果如下：

ts_resample             unit    Val1    Val2
2020-12-01 00:00:00     unit1   0.8974  10.485
2020-12-01 00:00:00     unit2   0.8974  10.485
2020-12-01 00:00:00     unit3   0.8974  10.485
2020-12-01 00:05:00     unit1   0.9041  11.854
2020-12-01 00:05:00     unit2   0.9041  11.854
2020-12-01 00:05:00     unit3   0.9041  11.854

实际上我想得到每个单位的最后一个值，每个单位的值是不同的。如下所示：

ts_resample             unit    Val1    Val2
2020-12-01 00:00:00     unit1   0.8974  10.485
2020-12-01 00:00:00     unit2   0.9014  11.954
2020-12-01 00:00:00     unit3   0.7854  10.821
2020-12-01 00:05:00     unit1   0.9841  11.125
2020-12-01 00:05:00     unit2   0.8742  10.963
2020-12-01 00:05:00     unit3   0.9632  11.784

有人能告诉我我的问题是什么吗？
谢谢