Hadoop Hive查询:多连接

Question

如何在Hive中进行子选择？我想我可能会犯一个非常明显的错误,这对我来说并不那么明显......

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

这是我的三个源表:

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

...而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 :)

Answer 1

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

Hive仅在FROM子句中支持子查询.

您不能将子查询用作Hive中的"列".

要解决此问题,您需要在FROM子句中使用该子查询JOIN.(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)

有关在Hive中使用JOIN的更多信息,请查看https://cwiki.apache.org/confluence/display/Hive/LanguageManual+Joins.