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https://issues.apache.org/jira/browse/HIVE-13727?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15278165#comment-15278165
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Rajat Khandelwal commented on HIVE-13727:
-----------------------------------------
The rejection of the first query doesn't seem to be justified. It's a typical
top-n query, but the data is available in two tables. So an optimized way of
getting top-n is to get the top-n values from both tables and getting top-n
from 2n elements, instead of from the entire union of two tables.
> Getting error Failed rule: 'orderByClause clusterByClause distributeByClause
> sortByClause limitClause can only be applied to the whole union.' in subquery
> -----------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: HIVE-13727
> URL: https://issues.apache.org/jira/browse/HIVE-13727
> Project: Hive
> Issue Type: Bug
> Reporter: Rajat Khandelwal
>
> The error comes in the following query:
> {noformat}
> SELECT *
> FROM
> (SELECT *
> FROM srcpart a
> WHERE a.ds = '2008-04-08'
> AND a.hr = '11'
> ORDER BY a.key LIMIT 5
> UNION ALL
> SELECT *
> FROM srcpart b
> WHERE b.ds = '2008-04-08'
> AND b.hr = '14'
> ORDER BY b.key LIMIT 5) subq
> ORDER BY KEY LIMIT 5
> {noformat}
> But the following query works:
> {noformat}
> SELECT *
> FROM
> (SELECT *
> FROM
> (SELECT *
> FROM srcpart a
> WHERE a.ds = '2008-04-08'
> AND a.hr = '11'
> ORDER BY a.key LIMIT 5) pa
> UNION ALL SELECT *
> FROM
> (SELECT *
> FROM srcpart b
> WHERE b.ds = '2008-04-08'
> AND b.hr = '14'
> ORDER BY b.key LIMIT 5) pb) subq
> ORDER BY KEY LIMIT 5
> {noformat}
> The queries are logically identical, the query that's rejected has dummy
> select * clauses around the sub-queries.
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