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https://issues.apache.org/jira/browse/HIVE-6348?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16055603#comment-16055603
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Rui Li commented on HIVE-6348:
------------------------------
Hi [~ashutoshc], [~vgarg], either doing this in CBO or not is OK to me. But I'm
not sure how to handle cases like input20.q. Let's consider the following two
queries:
The orderBy should be removed in this one:
{code}
from (select key from src order by key) tmap insert overwrite table dest select
tmap.key;
{code}
While it shouldn't be removed in this one:
{code}
from (select key,value from src order by key,value) tmap insert overwrite table
dest1 reduce tmap.key, tmap.value using 'python input20_script.py';
{code}
The two queries have very similar ASTs. Any suggestions how can we distinguish
them? Maybe we can skip the optimization in case of scripts and UDFs. Is it
correct to expect a specific order from a sub query in the first place?
> Order by/Sort by in subquery
> ----------------------------
>
> Key: HIVE-6348
> URL: https://issues.apache.org/jira/browse/HIVE-6348
> Project: Hive
> Issue Type: Bug
> Reporter: Gunther Hagleitner
> Assignee: Rui Li
> Priority: Minor
> Labels: sub-query
> Attachments: HIVE-6348.1.patch, HIVE-6348.2.patch, HIVE-6348.3.patch
>
>
> select * from (select * from foo order by c asc) bar order by c desc;
> in hive sorts the data set twice. The optimizer should probably remove any
> order by/sort by in the sub query unless you use 'limit '. Could even go so
> far as barring it at the semantic level.
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