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https://issues.apache.org/jira/browse/CALCITE-1876?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16243441#comment-16243441
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Julian Hyde commented on CALCITE-1876:
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Reviewing and testing
https://github.com/apache/calcite/pull/562/commits/969b3e192711984138ae414f87d23428f4d9a5ff
now.
> Create a rule to push the projections used in aggregate functions
> -----------------------------------------------------------------
>
> Key: CALCITE-1876
> URL: https://issues.apache.org/jira/browse/CALCITE-1876
> Project: Calcite
> Issue Type: Improvement
> Components: csv-adapter
> Reporter: Luis Fernando Kauer
> Assignee: Julian Hyde
> Priority: Minor
>
> From Julian Hyde;
> "Calcite should realize that Aggregate has an implied Project (because it
> only uses a few columns) and push that projection into the CsvTableScan, but
> it doesn’t."
> A query scans only the used projection when no aggregation is used:
> sql->explain plan for select name from emps;
> CsvTableScan(table=[[SALES, EMPS]], fields=[[1]])
> But it scans all the projections when an aggregation is used:
> sql->explain plan for select max(name) from emps;
> EnumerableAggregate(group=[{}], EXPR$0=[MAX($1)])
> CsvTableScan(table=[[SALES, EMPS]], fields=[[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]])
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