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From "Amareshwari Sriramadasu (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-741) NULL is not handled correctly in join
Date Tue, 10 Aug 2010 07:37:16 GMT

    [ https://issues.apache.org/jira/browse/HIVE-741?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12896792#action_12896792
] 

Amareshwari Sriramadasu commented on HIVE-741:
----------------------------------------------

By adding logs to ExecReducer, I see that the input to reduce is the following:
{noformat}
{"key":{"joinkey0":null},"value":{"_col0":null,"_col1":35},"alias":0}
{"key":{"joinkey0":null},"value":{"_col0":12,"_col1":null},"alias":1}
{"key":{"joinkey0":10},"value":{"_col0":10,"_col1":1000},"alias":0}
{"key":{"joinkey0":10},"value":{"_col0":10,"_col1":100},"alias":0}
{"key":{"joinkey0":12},"value":{"_col0":12,"_col1":null},"alias":0}
{"key":{"joinkey0":35},"value":{"_col0":null,"_col1":35},"alias":1}
{"key":{"joinkey0":100},"value":{"_col0":100,"_col1":100},"alias":0}
{"key":{"joinkey0":100},"value":{"_col0":10,"_col1":100},"alias":1}
{"key":{"joinkey0":100},"value":{"_col0":100,"_col1":100},"alias":1}
{"key":{"joinkey0":1000},"value":{"_col0":10,"_col1":1000},"alias":1}
{noformat}

And joinkey with null values are processed under same group, I think they should be processed
in different groups, because comparison between nulls is not defined. 

> NULL is not handled correctly in join
> -------------------------------------
>
>                 Key: HIVE-741
>                 URL: https://issues.apache.org/jira/browse/HIVE-741
>             Project: Hadoop Hive
>          Issue Type: Bug
>            Reporter: Ning Zhang
>            Assignee: Ning Zhang
>
> With the following data in table input4_cb:
> Key        Value
> ------       --------
> NULL     325
> 18          NULL
> The following query:
> {code}
> select * from input4_cb a join input4_cb b on a.key = b.value;
> {code}
> returns the following result:
> NULL    325    18   NULL
> The correct result should be empty set.
> When 'null' is replaced by '' it works.

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