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Date: Fri, 20 May 2016 15:47:13 +0000 (UTC)
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Subject: [jira] [Commented] (DRILL-4679) CONVERT_FROM()  json format fails
 if 0 rows are received from upstream operator
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archived-at: Fri, 20 May 2016 15:47:15 -0000


    [ https://issues.apache.org/jira/browse/DRILL-4679?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15293579#comment-15293579 ] 

ASF GitHub Bot commented on DRILL-4679:
---------------------------------------

Github user jinfengni commented on a diff in the pull request:

    https://github.com/apache/drill/pull/504#discussion_r64063077
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/project/ProjectRecordBatch.java ---
    @@ -146,6 +159,27 @@ protected IterOutcome doWork() {
               if (next == IterOutcome.OUT_OF_MEMORY) {
                 outOfMemory = true;
                 return next;
    +          } else if (next == IterOutcome.NONE) {
    +            // since this is first batch and we already got a NONE, need to set up the schema
    +
    +            //allocate vv in the allocationVectors.
    +            for (final ValueVector v : this.allocationVectors) {
    --- End diff --
    
    the allocation logic may use existing method doAlloc().


> 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: Jinfeng Ni
>
> 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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