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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