[jira] [Created] (DRILL-3524) Drill proper DESCRIBE support for MongoDB

["Hari Sekhon (JIRA)" <ji...@apache.org>]

Hari Sekhon created DRILL-3524:
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             Summary: 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
    Affects Versions: 1.1.0
            Reporter: Hari Sekhon
            Assignee: Steven Phillips


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}+--------------+------------+--------------+
| COLUMN_NAME  | DATA_TYPE  | IS_NULLABLE  |
+--------------+------------+--------------+
| *            | 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?



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