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https://issues.apache.org/jira/browse/HIVE-16291?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15959604#comment-15959604
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Aihua Xu commented on HIVE-16291:
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That's much cleaner. +1.
> Hive fails when unions a parquet table with itself
> --------------------------------------------------
>
> Key: HIVE-16291
> URL: https://issues.apache.org/jira/browse/HIVE-16291
> Project: Hive
> Issue Type: Bug
> Components: Hive
> Reporter: Yibing Shi
> Assignee: Yibing Shi
> Attachments: HIVE-16291.1.patch, HIVE-16291.2.patch
>
>
> Reproduce commands:
> {code:sql}
> create table tst_unin (col1 int) partitioned by (p_tdate int) stored as
> parquet;
> insert into tst_unin partition (p_tdate=201603) values (20160312), (20160310);
> insert into tst_unin partition (p_tdate=201604) values (20160412), (20160410);
> select count(*) from (select tst_unin.p_tdate from tst_unin where
> tst_unin.col1=20160302 union all select tst_unin.p_tdate from tst_unin) t1;
> {code}
> The table is stored in Parquet format, which is a columnar file format. Hive
> tries to push the query predicates to the table scan operators so that only
> the needed columns are read. This is done by adding the needed column IDs
> into job configuration with property "hive.io.file.readcolumn.ids".
> In above case, the query unions the result of 2 subqueries, which select data
> from one same table. The first subquery doesn't need any column from Parquet
> file, while the second subquery needs a column "col1". Hive has a bug here,
> it finally set "hive.io.file.readcolumn.ids" to a value like "0,,0", which
> method ColumnProjectionUtils.getReadColumnIDs cannot parse.
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