Jesus Camacho Rodriguez created HIVE-18680:
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             Summary: FieldTrimmer missing opportunity with SortLimit operators
                 Key: HIVE-18680
                 URL: https://issues.apache.org/jira/browse/HIVE-18680
             Project: Hive
          Issue Type: Bug
          Components: CBO
    Affects Versions: 3.0.0
            Reporter: Jesus Camacho Rodriguez
            Assignee: Jesus Camacho Rodriguez


In the following plan, {{_o__col4}} is not needed:

{code}
2018-02-11T11:35:14,501 DEBUG [0fda1a20-c7f1-489e-b287-65f35fda9848 main] 
calcite.sql2rel: Plan after trimming unused fields
HiveProject(download_volume_bytes=[$0], ri_date=[$1], end_cell_id=[$2], 
environment=[$3])
  HiveSortLimit(sort0=[$2], dir0=[ASC-nulls-first], fetch=[100])
    HiveProject(download_volume_bytes=[$4], ri_date=[$3], end_cell_id=[$1], 
environment=[$2], _o__col4=[$0])
      HiveAggregate(group=[{0, 1, 2, 3}], agg#0=[sum($4)])
        HiveProject($f0=[$1], $f1=[$2], $f2=[$3], $f3=[$0], $f4=[$4])
          HiveProject(ri_date=[$0], imsi=[$1], end_cell_id=[$2], 
environment=[$3], s1_u_download_data_volume=[$4])
            HiveTableScan(table=[[default.lsr094]], table:alias=[a])
{code}

{{_o__col4}} should be removed by the FieldTrimmer. Otherwise, this may prevent 
MV rewriting to be triggered on some queries containing order by/limit clauses.



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