druid/docs/tutorials/tutorial-transform.md

id	title	sidebar_label
tutorial-transform	Transform input data	Transform input data

This tutorial demonstrates how to transform input data during ingestion.

Prerequisite

Before proceeding, download Apache Druid® as described in Quickstart (local) and have it running on your local machine. You don't need to load any data into the Druid cluster.

You should be familiar with data querying in Druid. If you haven't already, go through the Query data tutorial first.

Sample data

For this tutorial, you use the following sample data:

{"timestamp":"2018-01-01T07:01:35Z", "animal":"octopus", "location":1, "number":100}
{"timestamp":"2018-01-01T05:01:35Z", "animal":"mongoose", "location":2,"number":200}
{"timestamp":"2018-01-01T06:01:35Z", "animal":"snake", "location":3, "number":300}
{"timestamp":"2018-01-01T01:01:35Z", "animal":"lion", "location":4, "number":300}

Transform data during ingestion

Load the sample dataset using the INSERT INTO statement and the EXTERN function to ingest the data inline. In the Druid web console, go to the Query view and run the following query:

INSERT INTO "transform_tutorial"
WITH "ext" AS (
  SELECT *
  FROM TABLE(EXTERN('{"type":"inline","data":"{\"timestamp\":\"2018-01-01T07:01:35Z\",\"animal\":\"octopus\",  \"location\":1, \"number\":100}\n{\"timestamp\":\"2018-01-01T05:01:35Z\",\"animal\":\"mongoose\", \"location\":2,\"number\":200}\n{\"timestamp\":\"2018-01-01T06:01:35Z\",\"animal\":\"snake\", \"location\":3, \"number\":300}\n{\"timestamp\":\"2018-01-01T01:01:35Z\",\"animal\":\"lion\", \"location\":4, \"number\":300}"}', '{"type":"json"}')) EXTEND ("timestamp" VARCHAR, "animal" VARCHAR, "location" BIGINT, "number" BIGINT)
)
SELECT
  TIME_PARSE("timestamp") AS "__time",
  TEXTCAT('super-', "animal") AS "animal",
  "location",
  "number",
  "number" * 3 AS "triple-number"
FROM "ext"
WHERE (TEXTCAT('super-', "animal") = 'super-mongoose' OR "location" = 3 OR "number" = 100)
PARTITIONED BY DAY

In the SELECT clause, you specify the following transformations:

• animal: prepends "super-" to the values in the animal column using the TEXTCAT function. Note that it only ingests the transformed data.
• triple-number: multiplies the number column by three and stores the results in a column named triple-number. Note that the query ingests both the original and the transformed data.

Additionally, the WHERE clause applies the following three OR operators so that the query only ingests the rows where at least one of the following conditions is true:

• TEXTCAT('super-', "animal") matches "super-mongoose"
• location matches 3
• number matches 100

Once a row passes the filter, the ingestion job applies the transformations. In this example, the filter selects the first three rows because each row meets at least one of the required OR conditions. For the selected rows, the ingestion job ingests the transformed animal column, the location column, and both the original number and the transformed triple-number column. The "lion" row doesn't meet any of the conditions, so it is not ingested or transformed.

Query the transformed data

In the web console, open a new tab in the Query view. Run the following query to view the ingested data:

SELECT * FROM "transform_tutorial"

Returns the following:

__time	animal	location	number	triple-number
2018-01-01T05:01:35.000Z	super-mongoose	2	200	600
2018-01-01T06:01:35.000Z	super-snake	3	300	900
2018-01-01T07:01:35.000Z	super-octopus	1	100	300

Notice how the "lion" row is missing, and how the other three rows that were ingested have transformations applied to them.

Learn more

See the following topics for more information:

• All functions for a list of functions that can be used to transform data.
• Transform spec reference to learn more about transforms in JSON-based batch ingestion.
• WHERE clause to learn how to specify filters in Druid SQL.