[jira] [Updated] (DRILL-4479) JsonReader should pick a less restrictive type when creating the default column

["Suresh Ollala (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/DRILL-4479?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Suresh Ollala updated DRILL-4479:
---------------------------------
    Reviewer: Chun Chang

> JsonReader should pick a less restrictive type when creating the default column
> -------------------------------------------------------------------------------
>
>                 Key: DRILL-4479
>                 URL: https://issues.apache.org/jira/browse/DRILL-4479
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Storage - JSON
>    Affects Versions: 1.5.0
>            Reporter: Aman Sinha
>            Assignee: Aman Sinha
>             Fix For: 1.7.0
>
>         Attachments: mostlynulls.json
>
>
> This JIRA is related to DRILL-3806 but has a narrower scope, so I decided to create separate one. 
> The JsonReader has the method ensureAtLeastOneField() (see https://github.com/apache/drill/blob/master/exec/java-exec/src/main/java/org/apache/drill/exec/vector/complex/fn/JsonReader.java#L91) that ensures that when no columns are found, create an empty one and it chooses to create a nullable int column.  One consequence is that queries of the following type fail:
> {noformat}
> select c1 from dfs.`mostlynulls.json`;
> ...
> ...
> | null  |
> | null  |
> Error: DATA_READ ERROR: Error parsing JSON - You tried to write a VarChar type when you are using a ValueWriter of type NullableIntWriterImpl.
> File  /Users/asinha/data/mostlynulls.json
> Record  4097
> {noformat}
> In this file the first 4096 rows have NULL values for c1 followed by rows that have a valid string.  
> It would be useful for the Json reader to choose a less restrictive type such as varchar in order to allow more types of queries to run.  



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