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From "Lefty Leverenz (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-12082) Null comparison for greatest and least operator
Date Mon, 11 Jul 2016 07:40:10 GMT

    [ https://issues.apache.org/jira/browse/HIVE-12082?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15370323#comment-15370323
] 

Lefty Leverenz commented on HIVE-12082:
---------------------------------------

I'm not sure either, but the doc should mention 1.3.0 so I'll add a TODOC1.3 label to HIVE-14189.
 Here's the doc link:

* [Mathematical Functions (greatest & least are at end of table) | https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDF#LanguageManualUDF-MathematicalFunctions]

> Null comparison for greatest and least operator
> -----------------------------------------------
>
>                 Key: HIVE-12082
>                 URL: https://issues.apache.org/jira/browse/HIVE-12082
>             Project: Hive
>          Issue Type: Bug
>          Components: UDF
>            Reporter: Szehon Ho
>            Assignee: Szehon Ho
>             Fix For: 2.0.0
>
>         Attachments: HIVE-12082.2.patch, HIVE-12082.patch
>
>
> In mysql comparisons if any of the entries are null, then the result is null.
> [https://dev.mysql.com/doc/refman/5.0/en/comparison-operators.html|https://dev.mysql.com/doc/refman/5.0/en/comparison-operators.html]
and [https://dev.mysql.com/doc/refman/5.0/en/type-conversion.html|https://dev.mysql.com/doc/refman/5.0/en/type-conversion.html].
> This can be demonstrated by the following mysql query:
> {noformat}
> mysql> select greatest(1, null) from test;
> +-------------------+
> | greatest(1, null) |
> +-------------------+
> |              NULL |
> +-------------------+
> 1 row in set (0.00 sec)
> mysql> select greatest(-1, null) from test;
> +--------------------+
> | greatest(-1, null) |
> +--------------------+
> |               NULL |
> +--------------------+
> 1 row in set (0.00 sec)
> {noformat}
> This is in contrast to Hive, where null are ignored in the comparisons.
> {noformat}
> hive> select greatest(null, 1) from test;
> OK
> 1
> {noformat}



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