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https://issues.apache.org/jira/browse/DRILL-4679?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15292742#comment-15292742
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ASF GitHub Bot commented on DRILL-4679:
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GitHub user amansinha100 opened a pull request:
https://github.com/apache/drill/pull/504
DRILL-4679: When convert() functions are present, ensure that Project…
…RecordBatch produces a schema even for empty result set.
Add unit tests
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/amansinha100/incubator-drill DRILL-4679
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/drill/pull/504.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #504
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commit 8342ddd3b2eb664bd67ed6f375bba3c22ec0b9a8
Author: Aman Sinha <[email protected]>
Date: 2016-05-17T21:35:06Z
DRILL-4679: When convert() functions are present, ensure that
ProjectRecordBatch produces a schema even for empty result set.
Add unit tests
----
> CONVERT_FROM() json format fails if 0 rows are received from upstream
> operator
> -------------------------------------------------------------------------------
>
> Key: DRILL-4679
> URL: https://issues.apache.org/jira/browse/DRILL-4679
> Project: Apache Drill
> Issue Type: Bug
> Components: Execution - Relational Operators
> Affects Versions: 1.6.0
> Reporter: Aman Sinha
> Assignee: Aman Sinha
>
> CONVERT_FROM() json format fails as below if the underlying Filter produces 0
> rows:
> {noformat}
> 0: jdbc:drill:zk=local> select convert_from('{"abc":"xyz"}', 'json') as x
> from cp.`tpch/region.parquet` where r_regionkey = 9999;
> Error: SYSTEM ERROR: IllegalStateException: next() returned NONE without
> first returning OK_NEW_SCHEMA [#16, ProjectRecordBatch]
> Fragment 0:0
> {noformat}
> If the conversion is applied as UTF8 format, the same query succeeds:
> {noformat}
> 0: jdbc:drill:zk=local> select convert_from('{"abc":"xyz"}', 'utf8') as x
> from cp.`tpch/region.parquet` where r_regionkey = 9999;
> +----+
> | x |
> +----+
> +----+
> No rows selected (0.241 seconds)
> {noformat}
> The reason for this is the special handling in the ProjectRecordBatch for
> JSON. The output schema is not known for this until the run time and the
> ComplexWriter in the Project relies on seeing the input data to determine the
> output schema - this could be a MapVector or ListVector etc.
> If the input data has 0 rows due to a filter condition, we should at least
> produce a default output schema, e.g an empty MapVector ? Need to decide a
> good default. Note that the CONVERT_FROM(x, 'json') could occur on 2
> branches of a UNION-ALL and if one input is empty while the other side is
> not, it may still cause incompatibility.
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