.. _parquet:

*******
Parquet
*******

BLUE supports ingesting data into BLUE from Parquet files. However, because it is an open-source column-oriented data storage format, you may want to retain your data on foreign Parquet files instead of ingesting it into BLUE. BLUE supports executing queries on foreign Parquet files.

Foreign Data Wrapper Prerequisites
==================================

Before proceeding, ensure the following Foreign Data Wrapper (FDW) prerequisites:

* **File Existence:** Verify that the file you are ingesting data from exists at the specified path.

* **Path Accuracy:** Confirm that all path elements are present and correctly spelled. Any inaccuracies may lead to data retrieval issues.
* **Bucket Access Permissions:** Ensure that you have the necessary access permissions to the bucket from which you are ingesting data. Lack of permissions can hinder the data retrieval process.

* **Wildcard Accuracy:** If using wildcards, double-check their spelling and configuration. Misconfigured wildcards may result in unintended data ingestion.

Preparing Your Parquet Files
============================

Prepare your source Parquet files according to the requirements described in the following table:

.. list-table:: 
   :widths: 40 5 20 20 20 20 5 5 5 5 10
   :header-rows: 1
   
   * -   BLUE Type →
         Parquet Source ↓
     - ``BOOL``
     - ``TINYINT``
     - ``SMALLINT``
     - ``INT``
     - ``BIGINT``
     - ``REAL``
     - ``DOUBLE``
     - ``TEXT`` [#f0]_
     - ``DATE``
     - ``DATETIME``
   * - ``BOOLEAN``
     - Supported 
     - 
     - 
     - 
     - 
     - 
     - 
     - 
     - 
     - 
   * - ``INT16``
     - 
     - 
     - Supported
     - 
     - 
     - 
     - 
     - 
     - 
     - 
   * - ``INT32``
     - 
     - 
     - 
     - Supported
     - 
     - 
     - 
     - 
     - 
     - 
   * - ``INT64``
     - 
     - 
     - 
     - 
     - Supported
     - 
     - 
     - 
     - 
     - 
   * - ``FLOAT``
     - 
     - 
     - 
     - 
     - 
     - Supported
     - 
     - 
     - 
     - 
   * - ``DOUBLE``
     - 
     - 
     - 
     - 
     - 
     - 
     - Supported
     - 
     - 
     - 
   * - ``BYTE_ARRAY`` / ``FIXED_LEN_BYTE_ARRAY`` [#f2]_
     - 
     - 
     - 
     - 
     - 
     - 
     - 
     - Supported
     - 
     - 
   * - ``INT96`` [#f3]_
     - 
     - 
     - 
     - 
     - 
     - 
     - 
     - 
     - 
     - Supported [#f4]_

* Your statements will succeed even if your Parquet file contains an unsupported type, such as ``enum``, ``uuid``, ``time``, ``json``, ``bson``, ``lists``, ``maps``, but the data is not referenced in the table (it does not appear in the :ref:`SELECT` query). If the column containing the unsupported type is referenced, an error message is displayed explaining that the type is not supported and that the column may be ommitted. For solutions to this error message, see more information in **Managing Unsupported Column Types** example in the **Example** section.

.. rubric:: Footnotes

.. [#f0] Text values include ``TEXT``

.. [#f2] With UTF8 annotation

.. [#f3] With ``TIMESTAMP_NANOS`` or ``TIMESTAMP_MILLIS`` annotation

.. [#f4] Any microseconds will be rounded down to milliseconds.



Creating a Table
================

Before loading data, you must build the CREATE TABLE to correspond with the file structure of the inserted table.

The example in this section is based on the source nba.parquet table shown below:

.. csv-table:: nba.parquet
   :file: nba-t10.csv
   :widths: auto
   :header-rows: 1 

The following example shows the correct file structure used to create the ``CREATE FOREIGN TABLE`` statement based on the nba.parquet table:

.. code-block:: postgres
   
	CREATE FOREIGN TABLE ext_nba (
	  Name TEXT,
	  Team TEXT,
	  Number BIGINT,
	  Position TEXT,
	  Age BIGINT,
	  Height TEXT,
	  Weight BIGINT,
	  College TEXT,
	  Salary FLOAT
	)
	WRAPPER
	  parquet_fdw
	OPTIONS
	  (LOCATION = 's3://sqream-docs/nba.parquet');

.. tip:: An exact match must exist between the BLUE and Parquet types. For unsupported column types, you can set the type to any type and exclude it from subsequent queries.

.. note:: The **nba.parquet** file is stored on S3 at ``s3://sqream-demo-data/nba.parquet``.


Best Practices
==============

Because foreign tables do not automatically verify the file integrity or structure, BLUE recommends manually verifying your table output when ingesting Parquet files into BLUE. This lets you determine if your table output is identical to your originally inserted table.

The following is an example of the output based on the **nba.parquet** table:

.. code-block:: psql
   
	SELECT * FROM ext_nba LIMIT 10;
	
	Name          | Team           | Number | Position | Age | Height | Weight | College           | Salary  
	--------------+----------------+--------+----------+-----+--------+--------+-------------------+---------
	Avery Bradley | Boston Celtics |      0 | PG       |  25 | 6-2    |    180 | Texas             |  7730337
	Jae Crowder   | Boston Celtics |     99 | SF       |  25 | 6-6    |    235 | Marquette         |  6796117
	John Holland  | Boston Celtics |     30 | SG       |  27 | 6-5    |    205 | Boston University |         
	R.J. Hunter   | Boston Celtics |     28 | SG       |  22 | 6-5    |    185 | Georgia State     |  1148640
	Jonas Jerebko | Boston Celtics |      8 | PF       |  29 | 6-10   |    231 |                   |  5000000
	Amir Johnson  | Boston Celtics |     90 | PF       |  29 | 6-9    |    240 |                   | 12000000
	Jordan Mickey | Boston Celtics |     55 | PF       |  21 | 6-8    |    235 | LSU               |  1170960
	Kelly Olynyk  | Boston Celtics |     41 | C        |  25 | 7-0    |    238 | Gonzaga           |  2165160
	Terry Rozier  | Boston Celtics |     12 | PG       |  22 | 6-2    |    190 | Louisville        |  1824360
	Marcus Smart  | Boston Celtics |     36 | PG       |  22 | 6-4    |    220 | Oklahoma State    |  3431040

.. note:: If your table output has errors, verify that the structure of the Parquet files correctly corresponds to the foreign table structure that you created.