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From "Paul Rogers (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (DRILL-5920) Drill incorrectly projects column aliases to scan operator
Date Wed, 01 Nov 2017 18:40:00 GMT

     [ https://issues.apache.org/jira/browse/DRILL-5920?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Paul Rogers resolved DRILL-5920.
    Resolution: Not A Bug

> Drill incorrectly projects column aliases to scan operator
> ----------------------------------------------------------
>                 Key: DRILL-5920
>                 URL: https://issues.apache.org/jira/browse/DRILL-5920
>             Project: Apache Drill
>          Issue Type: Bug
>    Affects Versions: 1.10.0
>            Reporter: Paul Rogers
>            Priority: Major
> The {{TestNewTextReader.ensureColumnNameDisplayedinError}} unit test runs this query:
> {code}
> select max(columns[1]) as col1
> from cp.`textinput/input1.csv`
> where col1 is not null
> {code}
> The following appears in the {{SubScan}} for the {{TextFormatPlugin}}:
> {noformat}
> [`col1`, `columns`[1]]
> {noformat}
> This is clearly wrong. The actual table column is {{columns}} (and, specifically, element
1.) {{col1} is an alias that should never have been pushed down to the data source because
the data source does not know about aliases.
> Further, the projection list makes no distinction between the "real" and "alias" columns,
so, to the data source, both look like real table columns.
> The current workaround is to create a nullable int column for {{col1}} which is, presumably,
replaced by a later projection operator.
> Because this behavior is wrong, we must think though all the possible failure cases and
how to handle them in this incorrect design. What if the alias matches an (expensive) table
column? What if the alias is the same as some base column in the same query?
> {code}
> SELECT a as b, b as c FROM ...
> {code}
> Incorrect name handling may work in many cases, but it does lead to problems because
the behavior is not following the accepted SQL standards.

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