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From "Jinfeng Ni (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DRILL-1499) Different column order could appear in the result set for a schema-less select * query, even there are no changing schemas.
Date Tue, 07 Oct 2014 21:29:35 GMT

     [ https://issues.apache.org/jira/browse/DRILL-1499?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Jinfeng Ni updated DRILL-1499:
------------------------------
    Attachment: 0001-DRILL-1499-Drill-return-same-column-order-for-a-sche.patch

> Different column order could appear in the result set for a schema-less select * query,
even there are no changing schemas.
> ---------------------------------------------------------------------------------------------------------------------------
>
>                 Key: DRILL-1499
>                 URL: https://issues.apache.org/jira/browse/DRILL-1499
>             Project: Apache Drill
>          Issue Type: Bug
>            Reporter: Jinfeng Ni
>            Assignee: Jinfeng Ni
>         Attachments: 0001-DRILL-1499-Drill-return-same-column-order-for-a-sche.patch
>
>
> For a select * query referring to a schema-less table, Drill could return different column,
depending on the physical operators the query involves:
> Q1:
> {code}
> select * from cp.`employee.json` limit 3;
> +-------------+------------+------------+------------+-------------+----------------+------------+---------------+------------+------------+------------+---------------+-----------------+----------------+------------+-----------------+
> | employee_id | full_name  | first_name | last_name  | position_id | position_title |
 store_id  | department_id | birth_date | hire_date  |   salary   | supervisor_id | education_level
| marital_status |   gender   | management_role |
> +-------------+------------+------------+------------+-------------+----------------+------------+---------------+------------+------------+------------+---------------+-----------------+----------------+------------+-----------------+
> {code}
> Q2:
> {code}
> select * from cp.`employee.json` order by last_name limit 3;
> +------------+---------------+-----------------+-------------+------------+------------+------------+------------+------------+-----------------+----------------+-------------+----------------+------------+------------+---------------+
> | birth_date | department_id | education_level | employee_id | first_name | full_name
 |   gender   | hire_date  | last_name  | management_role | marital_status | position_id |
position_title |   salary   |  store_id  | supervisor_id |
> +------------+---------------+-----------------+-------------+------------+------------+------------+------------+------------+-----------------+----------------+-------------+----------------+------------+------------+---------------+
> {code}
> The difference between Q1 and Q2 is the order by clause.  With order by clause in Q2,
Drill will sort the column names alphabetically, while for Q1, the column names are in the
same order as in the data source. 
> The underlying cause for such difference is that the sort or sort-based merger operator
would require canonicalization, since the incoming batches could contain different schemas.

>  However, it would be better that such canonicalization is used only when the incoming
batches have changing schemas. If all the incoming batches have identical schemas, no need
to sort the column orders.  With this fix, Drill will present the same column order in the
result set, for a schema-less select * query,  if there is no changing schemas from incoming
data sources. 



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