ektravel commented on code in PR #16515: URL: https://github.com/apache/druid/pull/16515#discussion_r1624984406
########## docs/tutorials/tutorial-latest-by.md: ########## @@ -0,0 +1,225 @@ +--- +id: tutorial-latest-by +title: Query for latest values +sidebar_label: Query for latest and deduplicated data +description: How to use LATEST_BY or deltas for up-to-date values +--- + +<!-- + ~ Licensed to the Apache Software Foundation (ASF) under one + ~ or more contributor license agreements. See the NOTICE file + ~ distributed with this work for additional information + ~ regarding copyright ownership. The ASF licenses this file + ~ to you under the Apache License, Version 2.0 (the + ~ "License"); you may not use this file except in compliance + ~ with the License. You may obtain a copy of the License at + ~ + ~ http://www.apache.org/licenses/LICENSE-2.0 + ~ + ~ Unless required by applicable law or agreed to in writing, + ~ software distributed under the License is distributed on an + ~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY + ~ KIND, either express or implied. See the License for the + ~ specific language governing permissions and limitations + ~ under the License. + --> + +This tutorial describes strategies in Apache Druid for use cases that might be handled by UPSERT in other databases. You can use the LATEST_BY aggregation at query time or "deltas" for numeric dimensions at insert time. + +The [Update data](./tutorial-update-data.md) tutorial demonstrates how to use batch operations to updadate data according to the timestamp, including UPSERT cases. However, with streaming data, you can potentially use LATEST_BY or deltas to satisfy requirements otherwise handled with updates. + +## Prerequisites + +Before you follow the steps in this tutorial, download Druid as described in the [Local quickstart](index.md) 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](../tutorials/tutorial-query.md) tutorial first. + +## Use LATEST_BY to retrieve updated values + +Sometimes you want to read the latest value of one dimension or measure as it relates to another dimension. In a transactional database, you might maintain dimension or measure using UPSERT, but in Druid you can append all updates or changes during ingestion. The LATEST_BY function lets you get the most recent value for the dimension with the following type of query: + +```sql +SELECT dimension, + LATEST_BY(changed_dimension, update_timestamp) +FROM my_table +GROUP BY 1 +``` + +For example, consider the following table of events that log the total number of points over for a user: + +| `__time` | `user_id`| `total_points`| +| --- | --- | --- | +| `2024-01-01T01:00:00.000Z`|`funny_bunny1`| 10 | +| `2024-01-01T01:05:00.000Z`|`funny_bunny1`| 30 | +| `2024-01-01T02:00:00.000Z`|`funny_bunny1`| 35 | +| `2024-01-01T02:00:00.000Z`|`silly_monkey2`| 30 | +| `2024-01-01T02:05:00.000Z`|`silly_monkey2`| 55 | +| `2024-01-01T03:00:00.000Z`|`funny_bunny1`| 40 | + +<details> +<summary>Insert sample data</summary> + +```sql +REPLACE INTO "latest_by_tutorial1" OVERWRITE ALL +WITH "ext" AS ( + SELECT * + FROM TABLE( + EXTERN( + '{"type":"inline","data":"{\"timestamp\":\"2024-01-01T01:00:00Z\",\"user_id\":\"funny_bunny1\", \"points\":10}\n{\"timestamp\":\"2024-01-01T01:05:00Z\",\"user_id\":\"funny_bunny1\", \"points\":30}\n{\"timestamp\": \"2024-01-01T02:00:00Z\",\"user_id\":\"funny_bunny1\", \"points\":35}\n{\"timestamp\":\"2024-01-01T02:00:00Z\",\"user_id\":\"silly_monkey2\", \"points\":30}\n{\"timestamp\":\"2024-01-01T02:05:00Z\",\"user_id\":\"silly_monkey2\", \"points\":55}\n{\"timestamp\":\"2024-01-01T03:00:00Z\",\"user_id\":\"funny_bunny1\", \"points\":40}"}', + '{"type":"json"}' + ) + ) EXTEND ("timestamp" VARCHAR, "user_id" VARCHAR, "points" BIGINT) +) +SELECT + TIME_PARSE("timestamp") AS "__time", + "user_id", + "points" +FROM "ext" +PARTITIONED BY DAY +``` +</details> + +The following query gives us most recent `points` value for each `user_id`: Review Comment: ```suggestion To retrieve the most recent `points` value for each `user_id`, run the following query in a new tab: ``` -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: commits-unsubscr...@druid.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: commits-unsubscr...@druid.apache.org For additional commands, e-mail: commits-h...@druid.apache.org
