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From Alfredo Serafini <ser...@gmail.com>
Subject Re: describe query support? (catalog metadata, etc)
Date Tue, 24 Oct 2017 11:09:13 GMT
Hi Chun thanks again for your time and the suggestions.

my attempt was indeed to create a view from a CSV, using casting on
columns (using TO_DATE, etc...), in order to find the corresponding
datatype when querying with DESCRIBE on the created view, but it does
not work in my experimentations unfortunately!

*example 1: using DESCRIBE on view*

Using a DESCRIBE on the created view I'm always obtaining an empty
table of results, with column names: "COLUMN_NAME | DATA_TYPE |
IS_NULLABLE", but no actual value at all.

*example 2: querying on INFORMATION_SCHEMA on view*

When on the other hand I'm trying to explore the same view in another
way, using a query like:

SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE (TABLE_NAME='my_table')
;

I'm obtaining something more, but still not enough.
The results in this case has column names: "TABLE_CATALOG |
TABLE_SCHEMA | TABLE_NAME | COLUMN_NAME | ORDINAL_POSITION |
COLUMN_DEFAULT | IS_NULLABLE | DATA_TYPE | CHARACTER_MAXIMUM_LENGTH |
CHARACTER_OCTET_LENGTH | NUMERIC_PRECISION | NUMERIC_PRECISION_RADIX |
NUMERIC_SCALE | DATETIME_PRECISION | INTERVAL_TYPE |
INTERVAL_PRECISION"

but the records contains "DATA_TYPE=ANY" for each field (!), including
the ones I've casted when creating the view.

I'm not sure if those two examples refers to what you suggested? Or
maybe there is some kind of configuration for correctly saving those
informations inside the JSON format of the view, in order to have them
available for DESCRIBE and INFORMATION_SCHEMA?

thanks again for any idea,
Alfredo

PS:


One last experiment was try to changing manually the type in the saved
my_view.view.drill JSON file, removing the corresponding .crc (or changes
will be ignored). In this experiment the example 2 seems to work (or at
least it does return the correct value for type, manually changed from JSON
- I didn't try that from JDBC), where DESCRIBE still no work.


Hi Alfredo, I do not fully understand what you are asking but you are right
> that drill store views in
> JSON format. After you create a view on top of your CSV file, you can
> DESCRIBE the view to
> get schema info if that's what you want. Sorry if I misunderstood your
> question.

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