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From "Arina Ielchiieva (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-5375) Nested loop join: return correct result for left join
Date Wed, 22 Mar 2017 16:49:41 GMT

    [ https://issues.apache.org/jira/browse/DRILL-5375?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15936657#comment-15936657
] 

Arina Ielchiieva commented on DRILL-5375:
-----------------------------------------

Also adding new planner optimization option planner.enable_join_optimization:

Currently only nested loop join allows non-equi join conditions usage.
During planning stage nested loop join will be chosen when non-equi join is detected and planner.enable_nljoin_for_scalar_only
set to false. Though query performance may not be the most optimal in such case, user may
use such workaround to execute queries with non-equi joins.
Nested loop join allows only INNER and LEFT join usage and implies that right input is smaller
that left input. During LEFT join when join optimization is enabled and detected that right
input is larger that left, join will be optimized: left and right inputs will be flipped and
LEFT join type will be changed to RIGHT one. If query contains non-equi joins, after such
optimization it will fail, since nested loop does not allow RIGHT join. In this case if user
accepts probability of non optimal performance, he may turn off join optimization. Turning
off join optimization, makes sense only if user are not sure that right output is less or
equal to left, otherwise join optimization can be left turned on.

Note: once hash and merge joins will allow non-equi join conditions, the need to turn off
join optimization may go away.

> Nested loop join: return correct result for left join
> -----------------------------------------------------
>
>                 Key: DRILL-5375
>                 URL: https://issues.apache.org/jira/browse/DRILL-5375
>             Project: Apache Drill
>          Issue Type: Bug
>    Affects Versions: 1.8.0
>            Reporter: Arina Ielchiieva
>            Assignee: Arina Ielchiieva
>              Labels: doc-impacting
>
> Mini repro:
> 1. Create 2 Hive tables with data
> {code}
> CREATE TABLE t1 (
>   FYQ varchar(999),
>   dts varchar(999),
>   dte varchar(999)
> )
> ROW FORMAT DELIMITED FIELDS TERMINATED BY ',';
> 2016-Q1,2016-06-01,2016-09-30
> 2016-Q2,2016-09-01,2016-12-31
> 2016-Q3,2017-01-01,2017-03-31
> 2016-Q4,2017-04-01,2017-06-30
> CREATE TABLE t2 (
>   who varchar(999),
>   event varchar(999),
>   dt varchar(999)
> )
> ROW FORMAT DELIMITED FIELDS TERMINATED BY ',';
> aperson,did somthing,2017-01-06
> aperson,did somthing else,2017-01-12
> aperson,had chrsitmas,2016-12-26
> aperson,went wild,2016-01-01
> {code}
> 2. Impala Query shows correct result
> {code}
> select t2.dt, t1.fyq, t2.who, t2.event
> from t2
> left join t1 on t2.dt between t1.dts and t1.dte
> order by t2.dt;
> +------------+---------+---------+-------------------+
> | dt         | fyq     | who     | event             |
> +------------+---------+---------+-------------------+
> | 2016-01-01 | NULL    | aperson | went wild         |
> | 2016-12-26 | 2016-Q2 | aperson | had chrsitmas     |
> | 2017-01-06 | 2016-Q3 | aperson | did somthing      |
> | 2017-01-12 | 2016-Q3 | aperson | did somthing else |
> +------------+---------+---------+-------------------+
> {code}
> 3. Drill query shows wrong results:
> {code}
> alter session set planner.enable_nljoin_for_scalar_only=false;
> use hive;
> select t2.dt, t1.fyq, t2.who, t2.event
> from t2
> left join t1 on t2.dt between t1.dts and t1.dte
> order by t2.dt;
> +-------------+----------+----------+--------------------+
> |     dt      |   fyq    |   who    |       event        |
> +-------------+----------+----------+--------------------+
> | 2016-12-26  | 2016-Q2  | aperson  | had chrsitmas      |
> | 2017-01-06  | 2016-Q3  | aperson  | did somthing       |
> | 2017-01-12  | 2016-Q3  | aperson  | did somthing else  |
> +-------------+----------+----------+--------------------+
> 3 rows selected (2.523 seconds)
> {code}



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