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From "B Anil Kumar (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-3524) Drill proper DESCRIBE support for MongoDB
Date Sun, 08 Nov 2015 14:24:10 GMT

    [ https://issues.apache.org/jira/browse/DRILL-3524?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14995645#comment-14995645

B Anil Kumar commented on DRILL-3524:

As Mongo collections doesn't have any schema. It doesn't make sense to implement this feature.

> Drill proper DESCRIBE support for MongoDB
> -----------------------------------------
>                 Key: DRILL-3524
>                 URL: https://issues.apache.org/jira/browse/DRILL-3524
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Metadata, Storage - MongoDB
>    Affects Versions: 1.1.0
>            Reporter: Hari Sekhon
>             Fix For: Future
> Request to add full DESCRIBE support for MongoDB collections.
> I understand this may be difficult / sub-optimal due to the flexible schema nature of
Mongo docs but if you can tabulate results when reading directly from MongoDB for which you
have read the field names, then it's also possible to extract all field names to present for
the describe command, albeit an inefficient scan to do so.
> Currently describe returns a pseudo / inaccurate / unhelpful metadata:
> {code}+--------------+------------+--------------+
> +--------------+------------+--------------+
> | *            | ANY        | YES          |
> +--------------+------------+--------------+{code}
> Perhaps you could extend DESCRIBE to scan the first few dozen docs by default to create
a merged schema as well as adding an optional argument to the describe command to allow for
scanning a user-specified number of docs from which to describe the schema, or an ALL argument
keyword to describe to scan all docs in a collection to get the complete global schema for
the collection?
> In case of schema evolution it might be an interesting option to additionally read the
newest and oldest records, maybe the first and last records by ID etc.

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