Hi David,
Your b.json file has only nulls; there is no way for Drill to determine what 
type of null is in your file. Drill requires each NULL to be a null of some 
type. Often, Drill guesses nullable int, which is why you saw the problem in 
your query.

If all your fields are strings, there is a workaround: use the "all-text-mode" 
when reading your JSON file. [1] Another workaround is to design the files so 
that the first record always has a non-null value for every field so Drill can 
guess the type correctly.

If any fields contain other types, you can use all text mode, then cast the 
non-text fields from text to the proper type.
 This is a known limitation: not just with Drill, but with any schema-free 
system. See DRILL-6035 [2].

At the present type, Drill supports no type of schema to help resolve this kind 
of ambiguity. (Though, having one would be the ideal solution to this kind of 

- Paul

[1] https://drill.apache.org/docs/json-data-model/

 [2] https://issues.apache.org/jira/browse/DRILL-6035

    On Friday, February 23, 2018, 12:04:01 PM PST, Lee, David 
<david....@blackrock.com> wrote:  
 Using Drill's CTAS statements I've run into a schema inconsistency issue and 
I'm not sure how to solve it..

CREATE TABLE name [ (column list) ] AS query;  

If I have a directory called Cities which have JSON files which look like:

{ "city":"San Francisco", "zip":"94105"}
{ "city":"San Jose", "zip":"94088"}

{ "city":"Toronto ", "zip": null}
{ "city":"Montreal", "zip" null}

If I create a parquet file out of the Cities directory I will end up with files 

1_0_0.parquet through 1_5_1.parquet

Now I got a problem:

Most of the parquet files have a column type of char for zip.
Some of the parquet files have a column type of int for zip because the zip 
value for a group of records was NULL..

This produces schema change errors later when trying to query the parquet 

Is it possible for Drill to do a better job learning schemas across all json 
files in a directory before creating parquet?

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