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https://issues.apache.org/jira/browse/CALCITE-1584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16031327#comment-16031327
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Arina Ielchiieva commented on CALCITE-1584:
-------------------------------------------
The reason I wanted to fix this rule is that in Drill we see the following
problem. For the query
{noformat}
select version as v from t
{noformat}
when during PHYSICAL phase ProjectRemoveRule is applied, it removes Project
stage and thus we lose column alias.
{noformat}
-------------------------------------------
| version<VARCHAR(OPTIONAL)> |
-------------------------------------------
| 1.10.0 |
-------------------------------------------
{noformat}
Query plan without ProjectRemoveRule
{noformat}
00-00 Screen
00-01 Project(v=[$0])
00-02 Scan(groupscan=[ParquetGroupScan [entries=[ReadEntryWithPath
[path=file:/tmp/t]], selectionRoot=/tmp/t, numFiles=1, usedMetadataFile=false,
columns=[`version`]]])
{noformat}
Query plan without ProjectRemoveRule
{noformat}
00-00 Screen
00-01 Scan(groupscan=[ParquetGroupScan [entries=[ReadEntryWithPath
[path=file:/tmp/t]], selectionRoot=/tmp/t, numFiles=1, usedMetadataFile=false,
columns=[`version`]]])
{noformat}
So I thought if I would add comparison to ProjectRemoveRule.isTrivial method by
field names as well, ProjectRemoveRule won't remove Project stage and thus
problem will be fixed.
Regarding r.getClass() I am not quite sure where I have to add it and how it
would help. So its not just a confusion, it's really I can't get what is
required to do for the fix if not changing isTrivial method. I am not a Calcite
expert, so sorry if some of my questions or assumptions are not correct. If you
could help to clarify what I can do for the fix, I'll really appreciate it.
> ProjectRemoveRule loses field names
> -----------------------------------
>
> Key: CALCITE-1584
> URL: https://issues.apache.org/jira/browse/CALCITE-1584
> Project: Calcite
> Issue Type: Bug
> Components: core
> Reporter: Jess Balint
> Assignee: Julian Hyde
> Priority: Minor
>
> the rule doesn't properly identify a child {{Project}} node
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