[jira] [Created] (DRILL-6313) ScanBatch.Mutator does not report new schema for empty first batch

["Paul Rogers (JIRA)" <ji...@apache.org>]

Paul Rogers created DRILL-6313:
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             Summary: ScanBatch.Mutator does not report new schema for empty first batch
                 Key: DRILL-6313
                 URL: https://issues.apache.org/jira/browse/DRILL-6313
             Project: Apache Drill
          Issue Type: Bug
    Affects Versions: 1.13.0
            Reporter: Paul Rogers
            Assignee: Paul Rogers
             Fix For: 1.14.0


Create a format plugin that honors an empty select list by returning no columns. This case occurs in a {{COUNT(\*)}} query.

When run, the query fails with:

{noformat}
SYSTEM ERROR: IllegalStateException: next() returned OK without first returning OK_NEW_SCHEMA [#2, ScanBatch]
{noformat}

The reason is that the {{Mutator}} class uses a flag, {{schemaChanged}}, which defaults to {{schemaChanged}}. It is set to {{true}} only when a field is added. But, since the query requested no fields, no field is added.

The fix is simple, just default {{schemaChanged}} to {{true}}.



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