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https://issues.apache.org/jira/browse/HIVE-9988?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15857435#comment-15857435
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Alexander Pivovarov commented on HIVE-9988:
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You can assign the expression to variable before query is evaluated and then
use the variable in WHERE
{code}
set dt=from_unixtime(unix_timestamp(),'yyyyMMdd');
select * from A where dt=${hiveconf:dt};
{code}
> Evaluating UDF before query is run
> ----------------------------------
>
> Key: HIVE-9988
> URL: https://issues.apache.org/jira/browse/HIVE-9988
> Project: Hive
> Issue Type: Improvement
> Reporter: Ådne Brunborg
>
> When using UDFs on partition column in Hive, all partitions are scanned
> before the UDF is resolved.
> If the UDF could be evaluated before query is run, this would greatly improve
> performance in cases like this.
> Example - the table has a partition by datestamp (bigint):
> The following where clause touches upon all 82 partitions:
> {{WHERE datestamp=cast(from_unixtime(unix_timestamp(),'yyyyMMdd') as bigint)}}
> {{15/03/16 09:21:53 INFO mapred.FileInputFormat: Total input paths to process
> : 82}}
> …whereas the following only touches the one partition:
> {{WHERE datestamp=20150316}}
> {{15/03/16 09:23:06 INFO input.FileInputFormat: Total input paths to process
> : 1}}
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