writer-jill commented on code in PR #12946: URL: https://github.com/apache/druid/pull/12946#discussion_r953576869
########## docs/querying/nested-columns.md: ########## @@ -0,0 +1,546 @@ +--- +id: nested-columns +title: "Nested columns" +sidebar_label: Nested columns +--- + +<!-- + ~ 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. + ~ + ~ Nested columns is an experimental feature that is subject to + ~ change or removal at any time. + --> + +> Nested columns is an experimental feature available starting in Apache Druid 24.0. As an experimental feature, functionality documented on this page is subject to change or removal in future releases. Review the release notes and this page to stay up to date with changes. + +You can ingest and store nested JSON in an Apache Druid column as a `COMPLEX<json>` data type. Druid indexes and optimizes the nested data. This means you can use JSON functions to extract ‘literal’ values at ingestion time using the `transformSpec` or in the SELECT clause when using multi-stage query architecture. + +Druid SQL JSON functions let you extract, transform, and create `COMPLEX<json>` values. Additionally, you can use certain `JSONPath` operators to extract values from nested data structures. + +Druid currently supports ingesting JSON-format nested columns with this feature. If you want to ingest nested data in another format, consider using the [flattenSpec object](../ingestion/data-formats.md#flattenspec). + +### Example nested data + +The examples in this topic use the data in [nested_example_data.json](https://static.imply.io/data/nested_example_data.json). The file contains a simple fascimile of an order tracking and shipping table. + +When pretty-printed a sample row in `nested_example_data` looks like this: + +```json +{ + "time":"2022-6-14T10:32:08Z", + "product":"Keyboard", + "department":"Computers", + "shipTo":{ + "firstName": "Sandra", + "lastName": "Beatty", + "address": { + "street": "293 Grant Well", + "city": "Loischester", + "state": "FL", + "country": "TV", + "postalCode": "88845-0066" + }, + "phoneNumbers": [ + {"type":"primary","number":"1-788-771-7028 x8627" }, + {"type":"secondary","number":"1-460-496-4884 x887"} + ] + }, + "details"{"color":"plum","price":"40.00"} +} +``` + +## Native batch ingestion + +For native batch ingestion, you can use the [JSON nested columns functions](../misc/math-expr.md#nested-columns-functions) to extract nested data as an alternative to using the [flattenSpec](../ingestion/data-formats.md#flattenspec) input format. + +To configure a dimension as a nested data type, include a `dimensions` object in the `dimensionsSpec` property of your ingestion spec. + +For example, the following ingestion spec instructs Druid to ingest `shipTo` and `details` as JSON-type nested dimensions: + +```json +{ + "type": "index_parallel", + "spec": { + "ioConfig": { + "type": "index_parallel", + "inputSource": { + "type": "http", + "uris": [ + "https://static.imply.io/data/nested_example_data.json"; + ] + }, + "inputFormat": { + "type": "json" + } + }, + "dataSchema": { + "granularitySpec": { + "segmentGranularity": "day", + "queryGranularity": "none", + "rollup": false + }, + "dataSource": "nested_data_example", + "timestampSpec": { + "column": "time", + "format": "auto" + }, + "dimensionsSpec": { + "dimensions": [ + "product", + "department", + { + "type": "json", + "name": "shipTo" + }, + { + "type": "json", + "name": "details" + } + ] + }, + "transformSpec": {} + }, + "tuningConfig": { + "type": "index_parallel", + "partitionsSpec": { + "type": "dynamic" + } + } + } +} +``` + +### Transform data during batch ingestion + +You can use the [JSON nested columns functions](../misc/math-expr.md#nested-columns-functions) to transform JSON data and reference the transformed data in your ingestion spec. + +To do this, include a `transforms` object in the `transformSpec` property of your ingestion spec. + +For example, the following ingestion spec extracts `firstName`, `lastName` and `address` from `shipTo` and creates a composite JSON object containing `product`, `details` and `department`. + +```json +{ + "type": "index_parallel", + "spec": { + "ioConfig": { + "type": "index_parallel", + "inputSource": { + "type": "http", + "uris": [ + "https://static.imply.io/data/nested_example_data.json"; + ] + }, + "inputFormat": { + "type": "json" + } + }, + "dataSchema": { + "granularitySpec": { + "segmentGranularity": "day", + "queryGranularity": "none", + "rollup": false + }, + "dataSource": "nested_data_transform_example", + "timestampSpec": { + "column": "time", + "format": "auto" + }, + "dimensionsSpec": { + "dimensions": [ + "firstName", + "lastName", + { + "type": "json", + "name": "address" + }, + { + "type": "json", + "name": "productDetails" + } + ] + }, + "transformSpec": { + "transforms":[ + { "type":"expression", "name":"firstName", "expression":"json_value(shipTo, '$.firstName')"}, + { "type":"expression", "name":"lastName", "expression":"json_value(shipTo, '$.lastName')"}, + { "type":"expression", "name":"address", "expression":"json_query(shipTo, '$.address')"}, + { "type":"expression", "name":"productDetails", "expression":"json_object('product', product, 'details', details, 'department', department)"} + ] + } + }, + "tuningConfig": { + "type": "index_parallel", + "partitionsSpec": { + "type": "dynamic" + } + } + } +} +``` + +## SQL-based ingestion + +To ingest nested data using multi-stage query architecture, specify `COMPLEX<json>` as the column `type` when you define the row signature—`shipTo` and `details` in the following example ingestion spec: + +> Note to self: add screenshot + +<!-----> + +```sql +REPLACE INTO msq_nested_data_example OVERWRITE ALL +SELECT + "time", + product, + department, + shipTo, + details +FROM ( + SELECT * FROM + TABLE( + EXTERN( + '{"type":"http","uris":["https://static.imply.io/data/nested_example_data.json"]}', + '{"type":"json"}', + '[{"name":"time","type":"string"},{"name":"product","type":"string"},{"name":"department","type":"string"},{"name":"shipTo","type":"COMPLEX<json>"},{"name":"details","type":"COMPLEX<json>"}]' + ) + ) +) +PARTITIONED BY ALL +``` + +### Transform data during SQL-based ingestion + +You can use the [JSON nested columns functions](../misc/math-expr.md#nested-columns-functions) to transform JSON data in your ingestion query. + +For example, the following ingestion query is the SQL-based version of the [batch example above](#transform-data-during-batch-ingestion)—it extracts `firstName`, `lastName` and `address` from `shipTo` and creates a composite JSON object containing `product`, `details` and `department`. + +```sql +REPLACE INTO msq_nested_data_transform_example OVERWRITE ALL +SELECT + "time", + JSON_VALUE(shipTo, '$.firstName') as firstName, + JSON_VALUE(shipTo, '$.lastName') as lastName, + JSON_QUERY(shipTo, '$.address') as address, + JSON_OBJECT('product':product,'details':details, 'department':department) as productDetails +FROM ( + SELECT * FROM + TABLE( + EXTERN( + '{"type":"http","uris":["https://static.imply.io/data/nested_example_data.json"]}', + '{"type":"json"}', + '[{"name":"time","type":"string"},{"name":"product","type":"string"},{"name":"department","type":"string"},{"name":"shipTo","type":"COMPLEX<json>"},{"name":"details","type":"COMPLEX<json>"}]' + ) + ) +) +PARTITIONED BY ALL +``` + +## Querying nested columns + +Once ingested, Druid stores the JSON-typed columns as native JSON objects and presents them as `COMPLEX<json>`. + +See the [Nested columns functions reference](../misc/math-expr.md#nested-columns-functions) for information on the functions in the examples below. + +### JSONPath syntax + +Druid supports a small, simplified subset of the [JSONPath syntax](https://github.com/json-path/JsonPath/blob/master/README.md) operators, primarily limited to extracting individual values from nested data structures. Review Comment: I think we should nominate a single location for the JSONPath syntax reference and link to it from the other relevant pages. Minimising duplication is our preferred approach. Suggest we keep it with the JSON functions reference, I remove it from this page and link to it? -- 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: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
