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https://issues.apache.org/jira/browse/IMPALA-14106?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17955550#comment-17955550
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Steve Carlin commented on IMPALA-14106:
---------------------------------------
Potentially it could help with partition key scans with according to this
specific comment:
"
We'll have to think about unions. It obviously can't do things like the count
star optimization, but some of the information is useful and can pass through.
(But that doesn't impact this review.)
For example: select count(*) from (select * from functional.alltypes union all
select * from functional.alltypestiny);
The regular planner doesn't change this into a partition key scan, but it
could: select distinct year from (select year from functional.alltypes union
all select year from functional.alltypessmall);
"
> Calcite planner: Register equivalent union expressions in value transfer graph
> ------------------------------------------------------------------------------
>
> Key: IMPALA-14106
> URL: https://issues.apache.org/jira/browse/IMPALA-14106
> Project: IMPALA
> Issue Type: Sub-task
> Reporter: Steve Carlin
> Priority: Major
>
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