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https://issues.apache.org/jira/browse/HIVE-746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13046837#comment-13046837
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Steven Wong commented on HIVE-746:
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For a query like:
select * from src where partcol = unix_timestamp();
Don't we want the expression unix_timestamp() to be evaluated once and to be
used in pruning the partitions, *whether the UDF unix_timestamp is marked
non-deterministic or not*?
> constant folding
> ----------------
>
> Key: HIVE-746
> URL: https://issues.apache.org/jira/browse/HIVE-746
> Project: Hive
> Issue Type: New Feature
> Components: Query Processor
> Reporter: Namit Jain
> Assignee: Zheng Shao
>
> The constants are not folded at compile time:
> for eg:
> select 1+2 from src
> will evaluate 1+2 for every row.
> This becomes more interesting for scenarios like:
> select unix_timestamp() from src;
> The UDF should be evaluated only once, and the same value should be returned.
> However, currently, we mark it as non-deterministic and evaluate it for every
> row.
> This can have bad side-effects on partition pruning etc.
> In MySQL, the same value is generated independent of the time taken for the
> query.
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