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https://issues.apache.org/jira/browse/DRILL-6791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16714000#comment-16714000
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ASF GitHub Bot commented on DRILL-6791:
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arina-ielchiieva commented on issue #1501: DRILL-6791: Scan projection framework
URL: https://github.com/apache/drill/pull/1501#issuecomment-445546658
+1, please squash the commits.
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> Merge scan projection framework into master
> -------------------------------------------
>
> Key: DRILL-6791
> URL: https://issues.apache.org/jira/browse/DRILL-6791
> Project: Apache Drill
> Issue Type: Improvement
> Affects Versions: 1.15.0
> Reporter: Paul Rogers
> Assignee: Paul Rogers
> Priority: Major
> Labels: ready-to-commit
> Fix For: 1.16.0
>
>
> Merge the next set of "result set loader" code into master via a PR. This one
> covers the "schema projection" mechanism which:
> * Handles none (SELECT COUNT\(*)), some (SELECT a, b, x) and all (SELECT *)
> projection.
> * Handles null columns (for projection a column "x" that does not exist in
> the base table.)
> * Handles constant columns as used for file metadata (AKA "implicit" columns).
> * Handle schema persistence: the need to reuse the same vectors across
> different scanners
> * Provides a framework for consuming externally-supplied metadata
> * Since we don't yet have a way to provide "real" metadata, obtains metadata
> hints from previous batches and from the projection list (a.b implies that
> "a" is a map, c[0] implies that "c" is an array, etc.)
> * Handles merging the set of data source columns and null columns to create
> the final output batch.
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