Question

如何在Hive中进行子选择？我想我可能犯了一个非常明显的错误，这对我来说并不那么明显......

我收到错误：FAILED: Parse Error: line 4:8 cannot recognize input 'SELECT' in expression specification

以下是我的三个源表：

aaa_hit -> [SESSION_KEY, HIT_KEY, URL]
aaa_event-> [SESSION_KEY,HIT_KEY,EVENT_ID]
aaa_session->[SESSION_KEY,REMOTE_ADDRESS]

...我想要做的是将结果插入到结果表中，如下所示：

result -> [url, num_url, event_id, num_event_id, remote_address, num_remote_address]

...其中第1列是URL，第3列是每个URL的前1个“事件”，第5列是访问该URL的前1个REMOTE_ADDRESS。（甚至列是前一列的“计数”。）

Soooooo ......我在这里做错了什么？

INSERT OVERWRITE TABLE result2
SELECT url, 
       COUNT(url) AS access_url, 
       (SELECT events.event_id as evt, 
               COUNT(events.event_id) as access_evt
        FROM   aaa_event events 
               LEFT OUTER JOIN aaa_hit hits 
                 ON ( events.hit_key = hit_key )
                 ORDER BY access_evt DESC LIMIT 1), 
       (SELECT sessions.remote_address as remote_address, 
               COUNT(sessions.remote_address) as access_addr
        FROM   aaa_session sessions 
               RIGHT OUTER JOIN aaa_hit hits 
                 ON ( sessions.session_key = session_key )
                 ORDER BY access_addr DESC LIMIT 1) 
FROM   aaa_hit
ORDER  BY access_url DESC;

非常感谢你：）

Answer 1

https://cwiki.apache.org/confluence/display/Hive/LanguageManual+SubQueries

Hive仅支持子查询 FROM子句。

您不能将子查询用作Hive中的“列”。

要解决此问题，您需要在FROM子句和JOIN中使用该子查询。（以下不起作用，但是这个想法）

SELECT url, 
       COUNT(url) AS access_url, 
       t2.col1, t2.col2 ...
FROM   aaa_hit
JOIN (SELECT events.event_id as evt, 
               COUNT(events.event_id) as access_evt
        FROM   aaa_event events 
               LEFT OUTER JOIN aaa_hit hits 
                 ON ( events.hit_key = hit_key )
                 ORDER BY access_evt DESC LIMIT 1), 
       (SELECT sessions.remote_address as remote_address, 
               COUNT(sessions.remote_address) as access_addr
        FROM   aaa_session sessions 
               RIGHT OUTER JOIN aaa_hit hits 
                 ON ( sessions.session_key = session_key )
                 ORDER BY access_addr DESC LIMIT 1) t2
ON (aaa_hit.THING = t2.THING)

查看https://cwiki.apache.org/confluence/display/Hive/LanguageManual+Joins以获取有关在Hive中使用JOIN的更多信息。

Answer 2

您没有GroupBy操作，Count是一个聚合。只有count（*）才能在没有GroupBy子句的情况下工作。

https://cwiki.apache.org/confluence/display/Hive/LanguageManual+GroupBy

Hadoop Hive查询：多连接

2 个答案: