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https://issues.apache.org/jira/browse/HIVE-284?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12672053#action_12672053
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Namit Jain commented on HIVE-284:
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Thats right - currently, column pruning is only on top of the base table i.e if
a column is not being used at all, it is removed right away
> Column pruning after join+group-by query
> ----------------------------------------
>
> Key: HIVE-284
> URL: https://issues.apache.org/jira/browse/HIVE-284
> Project: Hadoop Hive
> Issue Type: Improvement
> Affects Versions: 0.2.0, 0.3.0
> Reporter: Zheng Shao
>
> The query is:
> explain INSERT OVERWRITE TABLE t
> SELECT t1.r, t2.c, sum(t1.v * t2.v)
> FROM t1 join t2 on t1.c = t2.r
> GROUP BY t1.r, t2.c;
> The FileSinkOperator after the join is serializing all 6 columns from the 2
> tables (both have 3 columns: r, c, v) instead of the 4 that is needed later.
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