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https://issues.apache.org/jira/browse/DRILL-2173?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14308449#comment-14308449
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Jason Altekruse commented on DRILL-2173:
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https://reviews.apache.org/r/30701/
> Enable querying partition information without reading all data
> --------------------------------------------------------------
>
> Key: DRILL-2173
> URL: https://issues.apache.org/jira/browse/DRILL-2173
> Project: Apache Drill
> Issue Type: New Feature
> Components: Query Planning & Optimization
> Affects Versions: 0.7.0
> Reporter: Jason Altekruse
> Assignee: Jason Altekruse
> Attachments: Drill-2173-partition-queries-with-pruning.patch
>
>
> When reading a series of files in nested directories, Drill currently adds
> columns representing the directory structure that was traversed to reach the
> file currently being read. These columns are stored as varchar under tha
> names dir0, dir1, ... As these are just regular columns, Drill allows
> arbitrary queries against this data, in terms of aggregates, filter, sort,
> etc. To allow optimizing reads, basic partition pruning has already been
> added to prune in the case of an expression like dir0 = "2015" or a simple in
> list, which is converted during planning to a series of ORs of equals
> expressions. If users want to query the directory information dynamically,
> and not include specific directory names in the query, this will prompt a
> full table scan and filter operation on the dir columns. This enhancement is
> to allow more complex queries to be run against directory metadata, and only
> scanning the matching directories.
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