guiyanakuang commented on pull request #952:
URL: https://github.com/apache/orc/pull/952#issuecomment-964903950


   > > > @guiyanakuang I am wondering whether the selected vector only applies 
to the root struct-typed column vector. And I am curious if this patch is a 
part of some other big work items?
   > > 
   > > 
   > > @wgtmac Yes, the selected marker is at the row level. It will only work 
on the root. The purpose of this pr is to resolve 
[issue](https://issues.apache.org/jira/projects/ORC/issues/ORC-1004?filter=allopenissues).
 This feature helps me to write the results to the ORC file by filtering, which 
is useful for creating materialized views. It just happens to be useful for my 
current work, so I implemented it
   > 
   > As the selection vector only applies to the root struct type, is it 
possible to use null buffer of the root StructColumnVector (which is always not 
null for now)? We can ignore writing rows of null data there. This is much 
simpler but hacky.
   
   Sorry I didn't answer accurately, but in fact the root may also be a single 
column primitive type. Also the final VectorizedRowBatch obtained by filter 
query, the unselected rows may not be null. StructColumnVector seems to be 
written in such a way that it only appears when the sub-column type is struct. 


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