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https://issues.apache.org/jira/browse/DRILL-4185?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15051667#comment-15051667
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Khurram Faraaz commented on DRILL-4185:
---------------------------------------
On the other hand if we use an empty file (for example, an empty JSON file
named empty.json) in the directory named empty. UNION ALL returns results from
the non-empty input.
{code}
[root@centos-01 ~]# hadoop fs -ls /tmp/empty
Found 1 items
-rwxr-xr-x 3 root root 0 2015-11-04 23:43 /tmp/empty/empty.json
{code}
{code}
0: jdbc:drill:schema=dfs.tmp> select key1 from empty UNION ALL select EID from
Emp;
+-------+
| key1 |
+-------+
| 100 |
| 10 |
| 2 |
| 50 |
| 55 |
| 67 |
| 113 |
| 119 |
| 89 |
| 57 |
| 61 |
+-------+
11 rows selected (0.42 seconds)
{code}
> 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
>
> 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 ALL.
> 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}
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