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https://issues.apache.org/jira/browse/DRILL-2192?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Aman Sinha updated DRILL-2192:
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Assignee: Hanifi Gunes
> DrillScanRel should differentiate skip-all & scan-all & scan-some semantics
> while creating a GroupScan [umbrella]
> -----------------------------------------------------------------------------------------------------------------
>
> Key: DRILL-2192
> URL: https://issues.apache.org/jira/browse/DRILL-2192
> Project: Apache Drill
> Issue Type: Improvement
> Components: Query Planning & Optimization
> Reporter: Hanifi Gunes
> Assignee: Hanifi Gunes
> Fix For: 0.9.0
>
>
> DrillScanRel passes a list of columns to be read into GroupScan. Currently
> the logic here is to scan all of the columns even if planner asks to skip
> them all. Skipping all of the columns is particularly beneficial for the case
> of count(star) that is translated to count(constant) where we just need row
> count but not the actual data.
> The idea is to distinguish three separate states depending on the output
> coming from planner as follows:
> | list of columns from planner | scan semantics |
> | null | scan-all |
> | empty list of columns | skip-all |
> | non-empty list of columns w/o star | scan-some |
> | list of columns with star | scan-all |
> As part this umbrella, we should make readers understand skip-all semantics.
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