运行时，在FROM子句中获取错误“不匹配的输入”作为‘期望从附近’“

Question

我用java代码tableHiveCell和tableHiveWiFi创建了两个表。

当我尝试运行以下sql命令时：

select count(UEs.cnc) as 'Active UEs' 
                      ^
from 
(select distinct cnc from tableHiveCell wifi  
  union 
 select distinct cnc from tableHiveCell cell)
 as UEs;

我收到一个错误：

java.sql.SQLException:
Query returned non-zero code: 11,
cause: FAILED: Parse Error: line 1:22 mismatched input 'as' expecting FROM near ')' in from clause
at org.apache.hadoop.hive.jdbc.HiveStatement.executeQuery(HiveStatement.java:189).

我错过了什么吗？

编辑1

我试过：

select count(UEs.cnc) as 'Active UEs' 
                      ^
from 
(select distinct cnc from tableHiveCell wifi)  
  union 
 (select distinct cnc from tableHiveCell cell)
 as UEs;

相同误差

编辑2

我试过：

select count(UEs.cnc) as Active_UEs
 from (select distinct cnc from tableHiveCell wifi
  union ALL 
 select distinct cnc from tableHiveCell cell) as UEs;
                                              ^ 

获得相同的错误，但最后一个as

 line 1:142 mismatched input 'as' expecting Identifier near ')' in subquery source

Answer 1

按照应答表单中的请求: Hadoop似乎在子查询上通过AS关键字使用别名时遇到了问题，您可以轻松地分配别名而不使用AS关键字。

在这里可以找到示例：https://www.inkling.com/read/hadoop-definitive-guide-tom-white-3rd/chapter-12/querying-data

并为未来的访问者引用(子查询参见mt别名)：

SELECT station, year, AVG(max_temperature)
FROM (
  SELECT station, year, MAX(temperature) AS max_temperature
  FROM records2
  WHERE temperature != 9999
    AND (quality = 0 OR quality = 1 OR quality = 4 OR quality = 5 OR quality = 9)
  GROUP BY station, year
) mt
GROUP BY station, year;