两个查询的 Hive Union 给出编译错误

Question

我不确定下面的配置单元查询有什么问题。但是，它抛出错误。

select h.database_name, h.table_name, h.frequency as hive_frequency, i.frequency as impala_frequency    
from hive_access_frequency h
left join impala_access_frequency i
on 
h.database_name = i.database_name and 
h.table_name = i.table_name
union
select i.database_name, i.table_name, h.frequency as hive_frequency, i.frequency as impala_frequency    
from impala_access_frequency i
left join hive_access_frequency h
on 
h.database_name = i.database_name and 
h.table_name = i.table_name

我可以运行单独查询。但是，在 运行 union

时遇到问题

错误

Error: Error while compiling statement: FAILED: ParseException line 8:0 missing ALL at 'select' near '<EOF>' (state=42000,code=40000)

Answer 1

Hive versions prior to 1.2.0 only support UNION ALL

解决方法：使用 UNION ALL 而不是 UNION，将所有内容包装到子查询中并应用 distinct

select DISTINCT <column_list>
from
(
select ...
UNION ALL
select ...
)s;

UNION 与 UNION ALL + DISTINCT 相同