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id | title | sidebar_label |
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nested-columns | Nested columns | Nested columns |
Nested columns is an experimental feature available starting in Apache Druid 24.0. Like most experimental features, functionality documented on this page is subject to change in future releases. However, the COMPLEX column type includes versioning to provide backward compatible support in future releases. We strongly encourage you to experiment with nested columns in your development environment to evaluate that they meet your use case. If so, you can use them in production scenarios. Review the release notes and this page to stay up to date with changes.
Apache Druid supports directly storing nested data structures in COMPLEX<json>
columns. COMPLEX<json>
columns store a copy of the structured data in JSON format and specialized internal columns and indexes for nested literal values—STRING, LONG, and DOUBLE types. An optimized virtual column allows Druid to read and filter these values at speeds consistent with standard Druid LONG, DOUBLE, and STRING columns.
Druid SQL JSON functions allow you to extract, transform, and create COMPLEX<json>
values in SQL queries, using the specialized virtual columns where appropriate. You can use the JSON nested columns functions in native queries using expression virtual columns, and in native ingestion with a transformSpec
.
You can use the JSON functions in INSERT and REPLACE statements in SQL-based ingestion, or in a transformSpec
in native ingestion as an alternative to using a flattenSpec
object to "flatten" nested data for ingestion.
Example nested data
The examples in this topic use the data in nested_example_data.json
. The file contains a simple facsimile of an order tracking and shipping table.
When pretty-printed, a sample row in nested_example_data
looks like this:
{
"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 to extract nested data as an alternative to using the flattenSpec
input format.
To configure a dimension as a nested data type, specify the json
type for the dimension in the dimensions
list 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:
{
"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 to transform JSON data and reference the transformed data in your ingestion spec.
To do this, define the output name and expression in the transforms
list in the transformSpec
object 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
.
{
"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, '$.address')"},
{ "type":"expression", "name":"productDetails", "expression":"json_object('product', product, 'details', details, 'department', department)"}
]
}
},
"tuningConfig": {
"type": "index_parallel",
"partitionsSpec": {
"type": "dynamic"
}
}
}
}
SQL-based ingestion
To ingest nested data using multi-stage query architecture, specify COMPLEX<json>
as the value for type
when you define the row signature—shipTo
and details
in the following example ingestion spec:
REPLACE INTO msq_nested_data_example OVERWRITE ALL
SELECT
TIME_PARSE("time") as __time,
product,
department,
shipTo,
details
FROM (
SELECT * FROM
TABLE(
EXTERN(
'{"type":"http","uris":["https://static.imply.io/data/nested_example_data.json"]}',
'{"type":"json"}',
'[{"name":"time","type":"string"},{"name":"product","type":"string"},{"name":"department","type":"string"},{"name":"shipTo","type":"COMPLEX<json>"},{"name":"details","type":"COMPLEX<json>"}]'
)
)
)
PARTITIONED BY ALL
Transform data during SQL-based ingestion
You can use the JSON nested columns functions to transform JSON data in your ingestion query.
For example, the following ingestion query is the SQL-based version of the previous batch example—it extracts firstName
, lastName
, and address
from shipTo
and creates a composite JSON object containing product
, details
, and department
.
REPLACE INTO msq_nested_data_transform_example OVERWRITE ALL
SELECT
TIME_PARSE("time") as __time,
JSON_VALUE(shipTo, '$.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
Ingest a JSON string as COMPLEX<json>
If your source data uses a string representation of your JSON column, you can still ingest the data as COMPLEX<JSON>
as follows:
- During native batch ingestion, call the
parse_json
function in atransform
object in thetransformSpec
. - During SQL-based ingestion, use the PARSE_JSON keyword within your SELECT statement to transform the string values to JSON.
- If you are concerned that your data may not contain valid JSON, you can use
try_parse_json
for native batch orTRY_PARSE_JSON
for SQL-based ingestion. For cases where the column does not contain valid JSON, Druid inserts a null value.
If you are using a text input format like tsv
, you need to use this method to ingest data into a COMPLEX<json>
column.
For example, consider the following deserialized row of the sample data set:
{"time": "2022-06-13T10:10:35Z", "product": "Bike", "department":"Sports", "shipTo":"{\"firstName\": \"Henry\",\"lastName\": \"Wuckert\",\"address\": {\"street\": \"5643 Jan Walk\",\"city\": \"Lake Bridget\",\"state\": \"HI\",\"country\":\"ME\",\"postalCode\": \"70204-2939\"},\"phoneNumbers\": [{\"type\":\"primary\",\"number\":\"593.475.0449 x86733\" },{\"type\":\"secondary\",\"number\":\"638-372-1210\"}]}", "details":"{\"color\":\"ivory\", \"price\":955.00}"}
The following examples demonstrate how to ingest the shipTo
and details
columns both as string type and as COMPLEX<json>
in the shipTo_parsed
and details_parsed
columns.
REPLACE INTO deserialized_example OVERWRITE ALL
WITH source AS (SELECT * FROM TABLE(
EXTERN(
'{"type":"inline","data":"{\"time\": \"2022-06-13T10:10:35Z\", \"product\": \"Bike\", \"department\":\"Sports\", \"shipTo\":\"{\\\"firstName\\\": \\\"Henry\\\",\\\"lastName\\\": \\\"Wuckert\\\",\\\"address\\\": {\\\"street\\\": \\\"5643 Jan Walk\\\",\\\"city\\\": \\\"Lake Bridget\\\",\\\"state\\\": \\\"HI\\\",\\\"country\\\":\\\"ME\\\",\\\"postalCode\\\": \\\"70204-2939\\\"},\\\"phoneNumbers\\\": [{\\\"type\\\":\\\"primary\\\",\\\"number\\\":\\\"593.475.0449 x86733\\\" },{\\\"type\\\":\\\"secondary\\\",\\\"number\\\":\\\"638-372-1210\\\"}]}\", \"details\":\"{\\\"color\\\":\\\"ivory\\\", \\\"price\\\":955.00}\"}\n"}',
'{"type":"json"}',
'[{"name":"time","type":"string"},{"name":"product","type":"string"},{"name":"department","type":"string"},{"name":"shipTo","type":"string"},{"name":"details","type":"string"}]'
)
))
SELECT
TIME_PARSE("time") AS __time,
"product",
"department",
"shipTo",
"details",
PARSE_JSON("shipTo") as "shipTo_parsed",
PARSE_JSON("details") as "details_parsed"
FROM source
PARTITIONED BY DAY
"type": "index_parallel",
"spec": {
"ioConfig": {
"type": "index_parallel",
"inputSource": {
"type": "inline",
"data": "{\"time\": \"2022-06-13T10:10:35Z\", \"product\": \"Bike\", \"department\":\"Sports\", \"shipTo\":\"{\\\"firstName\\\": \\\"Henry\\\",\\\"lastName\\\": \\\"Wuckert\\\",\\\"address\\\": {\\\"street\\\": \\\"5643 Jan Walk\\\",\\\"city\\\": \\\"Lake Bridget\\\",\\\"state\\\": \\\"HI\\\",\\\"country\\\":\\\"ME\\\",\\\"postalCode\\\": \\\"70204-2939\\\"},\\\"phoneNumbers\\\": [{\\\"type\\\":\\\"primary\\\",\\\"number\\\":\\\"593.475.0449 x86733\\\" },{\\\"type\\\":\\\"secondary\\\",\\\"number\\\":\\\"638-372-1210\\\"}]}\", \"details\":\"{\\\"color\\\":\\\"ivory\\\", \\\"price\\\":955.00}\"}\n"
},
"inputFormat": {
"type": "json"
}
},
"tuningConfig": {
"type": "index_parallel",
"partitionsSpec": {
"type": "dynamic"
}
},
"dataSchema": {
"dataSource": "deserialized_example",
"timestampSpec": {
"column": "time",
"format": "iso"
},
"transformSpec": {
"transforms": [
{
"type": "expression",
"name": "shipTo_parsed",
"expression": "parse_json(shipTo)"
},
{
"type": "expression",
"name": "details_parsed",
"expression": "parse_json(details)"
}
]
},
"dimensionsSpec": {
"dimensions": [
"product",
"department",
"shipTo",
"details",
"shipTo_parsed",
"details_parsed"
]
},
"granularitySpec": {
"queryGranularity": "none",
"rollup": false,
"segmentGranularity": "day"
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 for information on the functions in the examples below.
Druid supports a small, simplified subset of the JSONPath syntax operators, primarily limited to extracting individual values from nested data structures. See the SQL JSON functions page for details.
Displaying data types
The following example illustrates how you can display the data types for your columns. Note that details
and shipTo
display as COMPLEX<json>
.
Example query: Display data types
SELECT TABLE_NAME, COLUMN_NAME, DATA_TYPE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'nested_data_example'
Example query results:
[["TABLE_NAME","COLUMN_NAME","DATA_TYPE"],["STRING","STRING","STRING"],["VARCHAR","VARCHAR","VARCHAR"],["nested_data_example","__time","TIMESTAMP"],["nested_data_example","department","VARCHAR"],["nested_data_example","details","COMPLEX<json>"],["nested_data_example","product","VARCHAR"],["nested_data_example","shipTo","COMPLEX<json>"]]
Retrieving JSON data
You can retrieve JSON data directly from a table. Druid returns the results as a JSON object, so you can't use grouping, aggregation, or filtering operators.
Example query: Retrieve JSON data
The following example query extracts all data from nested_data_example
:
SELECT * FROM nested_data_example
Example query results:
[["__time","department","details","product","shipTo"],["LONG","STRING","COMPLEX<json>","STRING","COMPLEX<json>"],["TIMESTAMP","VARCHAR","OTHER","VARCHAR","OTHER"],["2022-06-13T07:52:29.000Z","Sports","{\"color\":\"sky blue\",\"price\":542.0}","Bike","{\"firstName\":\"Russ\",\"lastName\":\"Cole\",\"address\":{\"street\":\"77173 Rusty Station\",\"city\":\"South Yeseniabury\",\"state\":\"WA\",\"country\":\"BL\",\"postalCode\":\"01893\"},\"phoneNumbers\":[{\"type\":\"primary\",\"number\":\"891-374-6188 x74568\"},{\"type\":\"secondary\",\"number\":\"1-248-998-4426 x33037\"}]}"],["2022-06-13T10:10:35.000Z","Sports","{\"color\":\"ivory\",\"price\":955.0}","Bike","{\"firstName\":\"Henry\",\"lastName\":\"Wuckert\",\"address\":{\"street\":\"5643 Jan Walk\",\"city\":\"Lake Bridget\",\"state\":\"HI\",\"country\":\"ME\",\"postalCode\":\"70204-2939\"},\"phoneNumbers\":[{\"type\":\"primary\",\"number\":\"593.475.0449 x86733\"},{\"type\":\"secondary\",\"number\":\"638-372-1210\"}]}"],["2022-06-13T13:57:38.000Z","Grocery","{\"price\":8.0}","Sausages","{\"firstName\":\"Forrest\",\"lastName\":\"Brekke\",\"address\":{\"street\":\"41548 Collier Divide\",\"city\":\"Wintheiserborough\",\"state\":\"WA\",\"country\":\"AD\",\"postalCode\":\"27577-6784\"},\"phoneNumbers\":[{\"type\":\"primary\",\"number\":\"(904) 890-0696 x581\"},{\"type\":\"secondary\",\"number\":\"676.895.6759\"}]}"],["2022-06-13T21:37:06.000Z","Computers","{\"color\":\"olive\",\"price\":90.0}","Mouse","{\"firstName\":\"Rickey\",\"lastName\":\"Rempel\",\"address\":{\"street\":\"6232 Green Glens\",\"city\":\"New Fermin\",\"state\":\"HI\",\"country\":\"CW\",\"postalCode\":\"98912-1195\"},\"phoneNumbers\":[{\"type\":\"primary\",\"number\":\"(689) 766-4272 x60778\"},{\"type\":\"secondary\",\"number\":\"375.662.4737 x24707\"}]}"],["2022-06-14T10:32:08.000Z","Computers","{\"color\":\"plum\",\"price\":40.0}","Keyboard","{\"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\"}]}"]]
Extracting nested data elements
The JSON_VALUE
function is specially optimized to provide native Druid level performance when processing nested literal values, as if they were flattened, traditional, Druid column types. It does this by reading from the specialized nested columns and indexes that are built and stored in JSON objects when Druid creates segments.
Some operations using JSON_VALUE
run faster than those using native Druid columns. For example, filtering numeric types uses the indexes built for nested numeric columns, which are not available for Druid DOUBLE, FLOAT, or LONG columns.
JSON_VALUE
only returns literal types. Any paths that reference JSON objects or array types return null.
To achieve the best possible performance, use the
JSON_VALUE
function whenever you query JSON objects.
Example query: Extract nested data elements
The following example query illustrates how to use JSON_VALUE
to extract specified elements from a COMPLEX<json>
object. Note that the returned values default to type VARCHAR.
SELECT
product,
department,
JSON_VALUE(shipTo, '$.address.country') as country,
JSON_VALUE(shipTo, '$.phoneNumbers[0].number') as primaryPhone,
JSON_VALUE(details, '$.price') as price
FROM nested_data_example
Example query results:
[["product","department","country","primaryPhone","price"],["STRING","STRING","STRING","STRING","STRING"],["VARCHAR","VARCHAR","VARCHAR","VARCHAR","VARCHAR"],["Bike","Sports","BL","891-374-6188 x74568","542.0"],["Bike","Sports","ME","593.475.0449 x86733","955.0"],["Sausages","Grocery","AD","(904) 890-0696 x581","8.0"],["Mouse","Computers","CW","(689) 766-4272 x60778","90.0"],["Keyboard","Computers","TV","1-788-771-7028 x8627","40.0"]]
Extracting nested data elements as a suggested type
You can use the RETURNING
keyword to provide type hints to the JSON_VALUE
function. This way the SQL planner produces the correct native Druid query, leading to expected results. This keyword allows you to specify a SQL type for the path
value.
Example query: Extract nested data elements as suggested types
The following example query illustrates how to use JSON_VALUE
and the RETURNING
keyword to extract an element of nested data and return it as specified types.
SELECT
product,
department,
JSON_VALUE(shipTo, '$.address.country') as country,
JSON_VALUE(details, '$.price' RETURNING BIGINT) as price_int,
JSON_VALUE(details, '$.price' RETURNING DECIMAL) as price_decimal,
JSON_VALUE(details, '$.price' RETURNING VARCHAR) as price_varchar
FROM nested_data_example
Query results:
[["product","department","country","price_int","price_decimal","price_varchar"],["STRING","STRING","STRING","LONG","DOUBLE","STRING"],["VARCHAR","VARCHAR","VARCHAR","BIGINT","DECIMAL","VARCHAR"],["Bike","Sports","BL",542,542.0,"542.0"],["Bike","Sports","ME",955,955.0,"955.0"],["Sausages","Grocery","AD",8,8.0,"8.0"],["Mouse","Computers","CW",90,90.0,"90.0"],["Keyboard","Computers","TV",40,40.0,"40.0"]]
Grouping, aggregating, and filtering
You can use JSON_VALUE
expressions in any context where you can use traditional Druid columns, such as grouping, aggregation, and filtering.
Example query: Grouping and filtering
The following example query illustrates how to use SUM, WHERE, GROUP BY, and ORDER BY operators with JSON_VALUE
.
SELECT
product,
JSON_VALUE(shipTo, '$.address.country'),
SUM(JSON_VALUE(details, '$.price' RETURNING BIGINT))
FROM nested_data_example
WHERE JSON_VALUE(shipTo, '$.address.country') in ('BL', 'CW')
GROUP BY 1,2
ORDER BY 3 DESC
Example query results:
[["product","EXPR$1","EXPR$2"],["STRING","STRING","LONG"],["VARCHAR","VARCHAR","BIGINT"],["Bike","BL",542],["Mouse","CW",90]]
Transforming JSON object data
In addition to JSON_VALUE
, Druid offers a number of operators that focus on transforming JSON object data:
JSON_QUERY
JSON_OBJECT
PARSE_JSON
TO_JSON_STRING
These functions are primarily intended for use with the multi-stage query architecture to transform data during insert operations, but they also work in traditional Druid SQL queries. Because most of these functions output JSON objects, they have the same limitations when used in traditional Druid queries as interacting with the JSON objects directly.
Example query: Return results in a JSON object
You can use the JSON_QUERY
function to extract a partial structure from any JSON input and return results in a JSON object. Unlike JSON_VALUE
it can extract objects and arrays.
The following example query illustrates the differences in output between JSON_VALUE
and JSON_QUERY
. The two output columns for JSON_VALUE
contain null values only because JSON_VALUE
only returns literal types.
SELECT
JSON_VALUE(shipTo, '$.address'),
JSON_QUERY(shipTo, '$.address'),
JSON_VALUE(shipTo, '$.phoneNumbers'),
JSON_QUERY(shipTo, '$.phoneNumbers')
FROM nested_data_example
Example query results:
[["EXPR$0","EXPR$1","EXPR$2","EXPR$3"],["STRING","COMPLEX<json>","STRING","COMPLEX<json>"],["VARCHAR","OTHER","VARCHAR","OTHER"],["","{\"street\":\"77173 Rusty Station\",\"city\":\"South Yeseniabury\",\"state\":\"WA\",\"country\":\"BL\",\"postalCode\":\"01893\"}","","[{\"type\":\"primary\",\"number\":\"891-374-6188 x74568\"},{\"type\":\"secondary\",\"number\":\"1-248-998-4426 x33037\"}]"],["","{\"street\":\"5643 Jan Walk\",\"city\":\"Lake Bridget\",\"state\":\"HI\",\"country\":\"ME\",\"postalCode\":\"70204-2939\"}","","[{\"type\":\"primary\",\"number\":\"593.475.0449 x86733\"},{\"type\":\"secondary\",\"number\":\"638-372-1210\"}]"],["","{\"street\":\"41548 Collier Divide\",\"city\":\"Wintheiserborough\",\"state\":\"WA\",\"country\":\"AD\",\"postalCode\":\"27577-6784\"}","","[{\"type\":\"primary\",\"number\":\"(904) 890-0696 x581\"},{\"type\":\"secondary\",\"number\":\"676.895.6759\"}]"],["","{\"street\":\"6232 Green Glens\",\"city\":\"New Fermin\",\"state\":\"HI\",\"country\":\"CW\",\"postalCode\":\"98912-1195\"}","","[{\"type\":\"primary\",\"number\":\"(689) 766-4272 x60778\"},{\"type\":\"secondary\",\"number\":\"375.662.4737 x24707\"}]"],["","{\"street\":\"293 Grant Well\",\"city\":\"Loischester\",\"state\":\"FL\",\"country\":\"TV\",\"postalCode\":\"88845-0066\"}","","[{\"type\":\"primary\",\"number\":\"1-788-771-7028 x8627\"},{\"type\":\"secondary\",\"number\":\"1-460-496-4884 x887\"}]"]]
Example query: Combine multiple JSON inputs into a single JSON object value
The following query illustrates how to use JSON_OBJECT
to combine nested data elements into a new object.
SELECT
JSON_OBJECT(KEY 'shipTo' VALUE JSON_QUERY(shipTo, '$'), KEY 'details' VALUE JSON_QUERY(details, '$')) as combinedJson
FROM nested_data_example
Example query results:
[["combinedJson"],["COMPLEX<json>"],["OTHER"],["{\"details\":{\"color\":\"sky blue\",\"price\":542.0},\"shipTo\":{\"firstName\":\"Russ\",\"lastName\":\"Cole\",\"address\":{\"street\":\"77173 Rusty Station\",\"city\":\"South Yeseniabury\",\"state\":\"WA\",\"country\":\"BL\",\"postalCode\":\"01893\"},\"phoneNumbers\":[{\"type\":\"primary\",\"number\":\"891-374-6188 x74568\"},{\"type\":\"secondary\",\"number\":\"1-248-998-4426 x33037\"}]}}"],["{\"details\":{\"color\":\"ivory\",\"price\":955.0},\"shipTo\":{\"firstName\":\"Henry\",\"lastName\":\"Wuckert\",\"address\":{\"street\":\"5643 Jan Walk\",\"city\":\"Lake Bridget\",\"state\":\"HI\",\"country\":\"ME\",\"postalCode\":\"70204-2939\"},\"phoneNumbers\":[{\"type\":\"primary\",\"number\":\"593.475.0449 x86733\"},{\"type\":\"secondary\",\"number\":\"638-372-1210\"}]}}"],["{\"details\":{\"price\":8.0},\"shipTo\":{\"firstName\":\"Forrest\",\"lastName\":\"Brekke\",\"address\":{\"street\":\"41548 Collier Divide\",\"city\":\"Wintheiserborough\",\"state\":\"WA\",\"country\":\"AD\",\"postalCode\":\"27577-6784\"},\"phoneNumbers\":[{\"type\":\"primary\",\"number\":\"(904) 890-0696 x581\"},{\"type\":\"secondary\",\"number\":\"676.895.6759\"}]}}"],["{\"details\":{\"color\":\"olive\",\"price\":90.0},\"shipTo\":{\"firstName\":\"Rickey\",\"lastName\":\"Rempel\",\"address\":{\"street\":\"6232 Green Glens\",\"city\":\"New Fermin\",\"state\":\"HI\",\"country\":\"CW\",\"postalCode\":\"98912-1195\"},\"phoneNumbers\":[{\"type\":\"primary\",\"number\":\"(689) 766-4272 x60778\"},{\"type\":\"secondary\",\"number\":\"375.662.4737 x24707\"}]}}"],["{\"details\":{\"color\":\"plum\",\"price\":40.0},\"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\"}]}}"]]
Using other transform functions
Druid provides the following additional transform functions:
PARSE_JSON
: Deserializes a string value into a JSON object.TO_JSON_STRING
: Performs the operation ofTO_JSON
and then serializes the value into a string.
Example query: Parse and deserialize data
The following query illustrates how to use the transform functions to parse and deserialize data.
SELECT
PARSE_JSON('{"x":"y"}'),
TO_JSON_STRING('{"x":"y"}'),
TO_JSON_STRING(PARSE_JSON('{"x":"y"}'))
Example query results:
[["EXPR$0","EXPR$2","EXPR$3"],["COMPLEX<json>","STRING","STRING"],["OTHER","VARCHAR","VARCHAR"],["{\"x\":\"y\"}","\"{\\\"x\\\":\\\"y\\\"}\"","{\"x\":\"y\"}"]]
Using helper operators
The JSON_KEYS
and JSON_PATHS
functions are helper operators that you can use to examine JSON object schema. Use them to plan your queries, for example to work out which paths to use in JSON_VALUE
.
Example query: Examine JSON object schema
The following query illustrates how to use the helper operators to examine a nested data object.
SELECT
ARRAY_CONCAT_AGG(DISTINCT JSON_KEYS(shipTo, '$.')),
ARRAY_CONCAT_AGG(DISTINCT JSON_KEYS(shipTo, '$.address')),
ARRAY_CONCAT_AGG(DISTINCT JSON_PATHS(shipTo))
FROM nested_data_example
Example query results:
[["EXPR$0","EXPR$1","EXPR$2","EXPR$3"],["COMPLEX<json>","COMPLEX<json>","STRING","STRING"],["OTHER","OTHER","VARCHAR","VARCHAR"],["{\"x\":\"y\"}","\"{\\\"x\\\":\\\"y\\\"}\"","\"{\\\"x\\\":\\\"y\\\"}\"","{\"x\":\"y\"}"]]
Known issues
Before you start using the nested columns feature, consider the following known issues:
- Directly using
COMPLEX<json>
columns and expressions is not well integrated into the Druid query engine. It can result in errors or undefined behavior when grouping and filtering, and when you useCOMPLEX<json>
objects as inputs to aggregators. As a workaround, consider usingTO_JSON_STRING
to coerce the values to strings before you perform these operations. - Directly using array-typed outputs from
JSON_KEYS
andJSON_PATHS
is moderately supported by the Druid query engine. You can group on these outputs, and there are a number of array expressions that can operate on these values, such asARRAY_CONCAT_AGG
. However, some operations are not well defined for use outside array-specific functions, such as filtering using=
orIS NULL
. - Input validation for JSON SQL operators is currently incomplete, which sometimes results in undefined behavior or unhelpful error messages.
- Ingesting JSON columns with a very complex nested structure is potentially an expensive operation and may require you to tune ingestion tasks and/or cluster parameters to account for increased memory usage or overall task run time. When you tune your ingestion configuration, treat each nested literal field inside a JSON object as a flattened top-level Druid column.
Further reading
For more information, see the following pages:
- Nested columns functions reference for details of the functions used in the examples on this page.
- Multi-stage query architecture overview for information on how to set up and use this feature.
- Ingestion spec reference for information on native ingestion and
transformSpec
. - Data formats for information on
flattenSpec
.