[jira] [Created] (DRILL-2192) DrillScanRel should differentiate skip-all & scan-all & scan-some semantics while creating a GroupScan [umbrella]

["Hanifi Gunes (JIRA)" <ji...@apache.org>]

Hanifi Gunes created DRILL-2192:
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             Summary: 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
            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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