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From "Ashish Thusoo (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-72) wrong results if partition pruning not strict and no mep-reduce job needed
Date Thu, 20 Nov 2008 22:14:44 GMT

    [ https://issues.apache.org/jira/browse/HIVE-72?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12649502#action_12649502

Ashish Thusoo commented on HIVE-72:


looks good to me.

> wrong results if partition pruning not strict and no mep-reduce job needed
> --------------------------------------------------------------------------
>                 Key: HIVE-72
>                 URL: https://issues.apache.org/jira/browse/HIVE-72
>             Project: Hadoop Hive
>          Issue Type: Bug
>            Reporter: Namit Jain
>            Assignee: Namit Jain
>         Attachments: patch1.mapred.txt
> Suppose T is a partitioned table on ds, where ds is a string column, the following queries:
>  SELECT a.* FROM T a WHERE a.ds=2008-09-08 LIMIT 1;
>  SELECT a.* FROM T a WHERE a.ds=2008-11-10 LIMIT 1;
> return the first row from the first partition.
> This is because of the typecast to double.
> for a.ds=2008-01-01 or anything (a.ds=1),
>  evaluate (Double, Double) is invoked at partition pruning.
> Since '2008-11-01' is not a valid double, it is converted to a null, and therefore the
result of pruning returns null (unknown) - not FALSE.
> All unknowns are also accepted, therefore all partitions are accepted which explains
this behavior.
> filter is not invoked since it is a select * query, so map-reduce job is started.
> We just turn off this optimization if pruning indicates that there can be unknown partitions.

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