[jira] Created: (HIVE-960) Lateral View optimizations

["Namit Jain (JIRA)" <ji...@apache.org>]

Lateral View optimizations
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                 Key: HIVE-960
                 URL: https://issues.apache.org/jira/browse/HIVE-960
             Project: Hadoop Hive
          Issue Type: New Feature
          Components: Query Processor
            Reporter: Namit Jain
            Assignee: Paul Yang


Had a offline discussion with Paul yesterday.


This is a followup on https://issues.apache.org/jira/browse/HIVE-935
Say, the query is 

select .. from T LATERAL VIEW explode(c2_list) as c2 LATERAL VIEW explode(c3_list) as c3


If we follow the suggestion from https://issues.apache.org/jira/browse/HIVE-935, 
(Lateral View Join operator will always have 2 inputs - the inputs will not be merged like join),
the explode operator for c3_list will be called once for each input on c2, which can be expensive.

Instead, if we merge the inputs and let LATERAL VIEW have 3 inputs, we will be invoking explode
operator for c3_list once for each row.

So, merging should be performed when the right side lateral views are not referencing anything from the
left side lateral views.

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