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From "Yongqiang He (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-560) column pruning not working with map joins
Date Sat, 20 Jun 2009 05:22:07 GMT

    [ https://issues.apache.org/jira/browse/HIVE-560?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12722143#action_12722143
] 

Yongqiang He commented on HIVE-560:
-----------------------------------

Some commets about the modification:
join is pruned by seeing which of its output column names is used by its children and pruned
unused exprs. 
And the join also remember which of the parent output columns it used for each parent reduce
sink. They are saved in the newly added field 'joinPrunedColLists' in pruner context. 
In reduce sink, if its child is a join, gets the information about which of its output is
used by the child join, and prunes itself accordingly.


> column pruning not working with map joins
> -----------------------------------------
>
>                 Key: HIVE-560
>                 URL: https://issues.apache.org/jira/browse/HIVE-560
>             Project: Hadoop Hive
>          Issue Type: Bug
>          Components: Query Processor
>    Affects Versions: 0.4.0
>            Reporter: Namit Jain
>            Assignee: Yongqiang He
>         Attachments: hive-560-2009-06-19-2.patch, hive-560-2009-06-19-5.patch
>
>
> drop table tst1;
> drop table tst2;
> create table tst1(a1 string, a2 string, a3 string, a4 string);
> create table tst2(b1 string, b2 string, b3 string, b4 string);
> explain select /*+ MAPJOIN(a) */ a.a1, a.a2 from tst1 a join tst2 b ON a.a2=b.b2;
> the select is after the join - column pruning is not happening

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