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https://issues.apache.org/jira/browse/DRILL-4783?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15386889#comment-15386889
 ] 

ASF GitHub Bot commented on DRILL-4783:
---------------------------------------

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

    https://github.com/apache/drill/pull/546#discussion_r71630375
  
    --- Diff: 
exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/flatten/FlattenRecordBatch.java
 ---
    @@ -129,11 +129,21 @@ private void setFlattenVector() {
         try {
           final TypedFieldId typedFieldId = 
incoming.getValueVectorId(popConfig.getColumn());
           final MaterializedField field = 
incoming.getSchema().getColumn(typedFieldId.getFieldIds()[0]);
    -      final RepeatedValueVector vector = 
RepeatedValueVector.class.cast(incoming.getValueAccessorById(
    -          field.getValueClass(), 
typedFieldId.getFieldIds()).getValueVector());
    +      RepeatedValueVector vector = null;
    +      try {
    +        vector = 
RepeatedValueVector.class.cast(incoming.getValueAccessorById(
    +            field.getValueClass(), 
typedFieldId.getFieldIds()).getValueVector());
    +      } catch(ClassCastException ex) {
    +        if(incoming.getRecordCount() != 0) {
    +          throw UserException.unsupportedError(ex).message("Flatten does 
not support inputs of non-list values.").build(logger);
    +        }
    +        //when incoming recordCount is 0, don't throw exception since the 
type being seen here is not solid
    +        logger.error("setFlattenVector cast failed and recordcount is 0, 
create empty vector anyway.");
    +        vector = new RepeatedMapVector(field, oContext.getAllocator(), 
null);
    +      }
           flattener.setFlattenField(vector);
         } catch (Exception ex) {
    -      throw UserException.unsupportedError(ex).message("Trying to flatten 
a non-repeated field.").build(logger);
    +      throw UserException.unsupportedError(ex).message("Flatten does not 
support inputs of non-list values.").build(logger);
    --- End diff --
    
    UserException may be thrown twice? Line 138 & Line 146. 


> Flatten on CONVERT_FROM fails with ClassCastException if resultset is empty
> ---------------------------------------------------------------------------
>
>                 Key: DRILL-4783
>                 URL: https://issues.apache.org/jira/browse/DRILL-4783
>             Project: Apache Drill
>          Issue Type: Bug
>            Reporter: Chunhui Shi
>            Assignee: Chunhui Shi
>            Priority: Critical
>
> Flatten failed to work on top of convert_from when the resultset is empty. 
> For a HBase table like this:
> 0: jdbc:drill:zk=localhost:5181> select convert_from(t.address.cities,'json') 
> from hbase.`/tmp/flattentest` t;
> +----------------------------------------------------------------------------------+
> |                                      EXPR$0                                 
>      |
> +----------------------------------------------------------------------------------+
> | {"list":[{"city":"SunnyVale"},{"city":"Palo Alto"},{"city":"Mountain 
> View"}]}    |
> | {"list":[{"city":"Seattle"},{"city":"Bellevue"},{"city":"Renton"}]}         
>      |
> | {"list":[{"city":"Minneapolis"},{"city":"Falcon Heights"},{"city":"San 
> Paul"}]}  |
> +----------------------------------------------------------------------------------+
> Flatten works when row_key is in (1,2,3)
> 0: jdbc:drill:zk=localhost:5181> select flatten(t1.json.list) from (select 
> convert_from(t.address.cities,'json') json from hbase.`/tmp/flattentest` t 
> where row_key=1) t1;
> +---------------------------+
> |          EXPR$0           |
> +---------------------------+
> | {"city":"SunnyVale"}      |
> | {"city":"Palo Alto"}      |
> | {"city":"Mountain View"}  |
> +---------------------------+
> But Flatten throws exception if the resultset is empty
> 0: jdbc:drill:zk=localhost:5181> select flatten(t1.json.list) from (select 
> convert_from(t.address.cities,'json') json from hbase.`/tmp/flattentest` t 
> where row_key=4) t1;
> Error: SYSTEM ERROR: ClassCastException: Cannot cast 
> org.apache.drill.exec.vector.NullableIntVector to 
> org.apache.drill.exec.vector.complex.RepeatedValueVector
> Fragment 0:0
> [Error Id: 07fd0cab-d1e6-4259-bfec-ad80f02d93a2 on atsqa4-127.qa.lab:31010] 
> (state=,code=0)



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