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Posted to issues@calcite.apache.org by "Chunwei Lei (JIRA)" <ji...@apache.org> on 2019/04/22 13:10:00 UTC

[jira] [Created] (CALCITE-3015) Add rule to remove constants in group keys

Chunwei Lei created CALCITE-3015:
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             Summary: Add rule to remove constants in group keys
                 Key: CALCITE-3015
                 URL: https://issues.apache.org/jira/browse/CALCITE-3015
             Project: Calcite
          Issue Type: Improvement
            Reporter: Chunwei Lei
            Assignee: Chunwei Lei


Constants in group keys can be removed to reduce shuffle. For instance, 

 
{code:java}
select key, count(*) from (select 1 as key from src) dual group by key;
{code}
can be reduced to
{code:java}
select count(*) from (select 1 as key from src) dual;{code}
It could save much resource in distribute system if all group keys are constants since the distribution becomes {{SINGLETON}} instead of {{HASH}}.



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