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https://issues.apache.org/jira/browse/HIVE-12082?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14951288#comment-14951288
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Sergey Shelukhin commented on HIVE-12082:
-----------------------------------------
compare predicates in ANSI SQL do evaluate to UNKNOWN, which is presumably
NULL. I wonder though if Hive evaluates the 3-value logic after that
correctly... anyway makes sense to change those to null
> 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
>
> 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 does not win in greatest, least over
> values.
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