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https://issues.apache.org/jira/browse/HIVE-11409?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14648123#comment-14648123
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Pengcheng Xiong commented on HIVE-11409:
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a good example is union_remove_10.q
{code}
Group By Operator
aggregations: count(VALUE._col0)
keys: KEY._col0 (type: string)
mode: mergepartial
outputColumnNames: $f0, $f1
Statistics: Num rows: 1 Data size: 30 Basic stats: COMPLETE Column
stats: NONE
Select Operator
expressions: $f0 (type: string), $f1 (type: bigint)
outputColumnNames: key, values
Statistics: Num rows: 1 Data size: 30 Basic stats: COMPLETE Column
stats: NONE
File Output Operator
compressed: false
Statistics: Num rows: 1 Data size: 30 Basic stats: COMPLETE
Column stats: NONE
table:
input format: org.apache.hadoop.hive.ql.io.RCFileInputFormat
output format: org.apache.hadoop.hive.ql.io.RCFileOutputFormat
serde: org.apache.hadoop.hive.serde2.columnar.ColumnarSerDe
name: default.outputtbl1
{code}
> CBO: Calcite Operator To Hive Operator (Calcite Return Path): add SEL before
> UNION
> ----------------------------------------------------------------------------------
>
> Key: HIVE-11409
> URL: https://issues.apache.org/jira/browse/HIVE-11409
> Project: Hive
> Issue Type: Sub-task
> Components: CBO
> Reporter: Pengcheng Xiong
> Assignee: Pengcheng Xiong
> Attachments: HIVE-11409.01.patch
>
>
> Two purpose: (1) to ensure that the data type of non-primary branch (the 1st
> branch is the primary branch) of union can be casted to that of the primary
> branch; (2) to make UnionProcessor optimizer work; (3) if the SEL is
> redundant, it will be removed by IdentidyProjectRemover optimizer.
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