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https://issues.apache.org/jira/browse/HIVE-20850?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16670864#comment-16670864
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Zoltan Haindrich commented on HIVE-20850:
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patch#1 also contains HIVE-20835
> Puse case conditional from projections to dimension tables if possible
> ----------------------------------------------------------------------
>
> Key: HIVE-20850
> URL: https://issues.apache.org/jira/browse/HIVE-20850
> Project: Hive
> Issue Type: Improvement
> Reporter: Zoltan Haindrich
> Assignee: Zoltan Haindrich
> Priority: Major
> Attachments: HIVE-20850.01.patch
>
>
> noticed by [~gopalv]: If there is a project which could be only evaluated
> after the join; but the condition references only a single column from a
> small dimension table; hive will end up evaluating the same thing over and
> over again...
> {code}
> explain
> select s_store_name, s_store_id,
> sum(case when (d_day_name='Sunday') then ss_sales_price else null
> end) sun_sales,
> sum(case when (d_day_name='Monday') then ss_sales_price else null
> end) mon_sales,
> sum(case when (d_day_name='Tuesday') then ss_sales_price else null
> end) tue_sales,
> sum(case when (d_day_name='Wednesday') then ss_sales_price else null
> end) wed_sales,
> sum(case when (d_day_name='Thursday') then ss_sales_price else null
> end) thu_sales,
> sum(case when (d_day_name='Friday') then ss_sales_price else null
> end) fri_sales,
> sum(case when (d_day_name='Saturday') then ss_sales_price else null
> end) sat_sales
> from date_dim, store_sales, store
> where d_date_sk = ss_sold_date_sk and
> s_store_sk = ss_store_sk and
> s_gmt_offset = -6 and
> d_year = 1998
> group by s_store_name, s_store_id
> order by s_store_name,
> s_store_id,sun_sales,mon_sales,tue_sales,wed_sales,thu_sales,fri_sales,sat_sales
> limit 100;
> {code}
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