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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-4185) UNION ALL involving empty directory on any side of union all results in Failed query
Date Wed, 31 Jan 2018 11:46:00 GMT

    [ https://issues.apache.org/jira/browse/DRILL-4185?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16346662#comment-16346662

ASF GitHub Bot commented on DRILL-4185:

Github user arina-ielchiieva commented on the issue:

    +1, LGTM. Thanks for making the changes.

> UNION ALL involving empty directory on any side of union all results in Failed query
> ------------------------------------------------------------------------------------
>                 Key: DRILL-4185
>                 URL: https://issues.apache.org/jira/browse/DRILL-4185
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Execution - Relational Operators
>    Affects Versions: 1.4.0
>            Reporter: Khurram Faraaz
>            Assignee: Vitalii Diravka
>            Priority: Major
>              Labels: doc-impacting
> UNION ALL query that involves an empty directory on either side of UNION ALL operator
results in FAILED query. We should return the results for the non-empty side (input) of UNION
> Note that empty_DIR is an empty directory, the directory exists, but it has no files
in it. 
> Drill 1.4 git.commit.id=b9068117
> 4 node cluster on CentOS
> {code}
> 0: jdbc:drill:schema=dfs.tmp> select columns[0] from empty_DIR UNION ALL select cast(columns[0]
as int) c1 from `testWindow.csv`;
> Error: VALIDATION ERROR: From line 1, column 24 to line 1, column 32: Table 'empty_DIR'
not found
> [Error Id: 5c024786-6703-4107-8a4a-16c96097be08 on centos-01.qa.lab:31010] (state=,code=0)
> 0: jdbc:drill:schema=dfs.tmp> select cast(columns[0] as int) c1 from `testWindow.csv`
UNION ALL select columns[0] from empty_DIR;
> Error: VALIDATION ERROR: From line 1, column 90 to line 1, column 98: Table 'empty_DIR'
not found
> [Error Id: 58c98bc4-99df-425c-aa07-c8c5faec4748 on centos-01.qa.lab:31010] (state=,code=0)
> {code}
> *Fix overview:*
> After resolving the current issue Drill can query an empty directory. It is a schemaless
Drill table for now. 
> User can query empty directory and use it for queries with any JOIN and UNION (UNION
ALL) operators.
> Empty directory with parquet metadata cache files is schemaless Drill table as well.

> It works similar to empty files:
> - The query with star will return empty result. 
> - If some fields are indicated in select statement, that fields will be returned as INT-OPTIONAL
> - The empty directory in the query with UNION operator will not change the result as
if the statement with UNION is absent in the query.
> -  The query with joins will return an empty result except the cases of using outer join
clauses, when the outer table for "right join" or derived table for "left join" has a data.
In that case the data from a non-empty table is returned.
> - The empty directory table can be used in complex queries.
> *Code changes:*
> Internally empty directory interprets as DynamicDrillTable with null selection. SchemalessScan,
SchemalessBatchCreator and SchemalessBatch are introduced and used on execution state for
interactions with other operators and batches.
> If empty directory contain parquet metadata cache files, the ParquetGroupScan for such
table is not valid and SchemalessScan is used instead of that.

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