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From "Jacques Nadeau (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DRILL-2192) DrillScanRel should differentiate skip-all & scan-all & scan-some semantics while creating a GroupScan [umbrella]
Date Mon, 23 Feb 2015 01:13:20 GMT

     [ https://issues.apache.org/jira/browse/DRILL-2192?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Jacques Nadeau updated DRILL-2192:
----------------------------------
    Component/s: Query Planning & Optimization

> 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
>
> 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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