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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-4539) Add support for Null Equality Joins
Date Wed, 06 Apr 2016 16:53:25 GMT

    [ https://issues.apache.org/jira/browse/DRILL-4539?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15228628#comment-15228628
] 

ASF GitHub Bot commented on DRILL-4539:
---------------------------------------

Github user vkorukanti commented on a diff in the pull request:

    https://github.com/apache/drill/pull/462#discussion_r58741416
  
    --- Diff: exec/java-exec/src/main/codegen/templates/ComparisonFunctions.java ---
    @@ -215,6 +192,36 @@ public void eval() {
         }
       }
     
    +  <#-- IS_DISTINCT_FROM function -->
    +  @FunctionTemplate(names = {"is_distinct_from", "is distinct from" },
    --- End diff --
    
    I am not sure if there is way to differentiate between the function in join condition
vs. function in project expr. I don't see any context info in DrillConvertletTable.get() method
call. Also the generated code in rewritten case is too much. For following query:
    ```SELECT INT_col is not distinct from BIGINT_col as col, int_distinct_result FROM cp.`functions/distinct_from.json```
    
    Without rewrite: https://gist.github.com/vkorukanti/e981058f985ed24e6c4ef6b47d670e0f
    With rewrite: https://gist.github.com/vkorukanti/d80aa2ba40c65c9215c38ed18b20a685
    
    Sizes may differ after scalar replacement is done, but it is still too much code to simple
```is not distinct from``` function. 
    



> Add support for Null Equality Joins
> -----------------------------------
>
>                 Key: DRILL-4539
>                 URL: https://issues.apache.org/jira/browse/DRILL-4539
>             Project: Apache Drill
>          Issue Type: Improvement
>            Reporter: Jacques Nadeau
>            Assignee: Venki Korukanti
>
> Tableau frequently generates queries similar to this:
> {code}
> SELECT `t0`.`city` AS `city`,
>   `t2`.`X_measure__B` AS `max_Calculation_DFIDBHHAIIECCJFDAG_ok`,
>   `t0`.`state` AS `state`,
>   `t0`.`sum_stars_ok` AS `sum_stars_ok`
> FROM (
>   SELECT `business`.`city` AS `city`,
>     `business`.`state` AS `state`,
>     SUM(`business`.`stars`) AS `sum_stars_ok`
>   FROM `mongo.academic`.`business` `business`
>   GROUP BY `business`.`city`,
>     `business`.`state`
> ) `t0`
>   INNER JOIN (
>   SELECT MAX(`t1`.`X_measure__A`) AS `X_measure__B`,
>     `t1`.`city` AS `city`,
>     `t1`.`state` AS `state`
>   FROM (
>     SELECT `business`.`city` AS `city`,
>       `business`.`state` AS `state`,
>       `business`.`business_id` AS `business_id`,
>       SUM(`business`.`stars`) AS `X_measure__A`
>     FROM `mongo.academic`.`business` `business`
>     GROUP BY `business`.`city`,
>       `business`.`state`,
>       `business`.`business_id`
>   ) `t1`
>   GROUP BY `t1`.`city`,
>     `t1`.`state`
> ) `t2` ON (((`t0`.`city` = `t2`.`city`) OR ((`t0`.`city` IS NULL) AND (`t2`.`city` IS
NULL))) AND ((`t0`.`state` = `t2`.`state`) OR ((`t0`.`state` IS NULL) AND (`t2`.`state` IS
NULL))))
> {code}
> If you look at the join condition, you'll note that the join condition is an equality
condition which also allows null=null. We should add a planning rewrite rule and execution
join option to allow null equality so that we don't treat this as a cartesian join.



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