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Getting started

  • Introduction to Apache Druid
  • Quickstart (local)
  • Single server deployment
  • Clustered deployment

Tutorials

  • Load files natively
  • Load files using SQL ๐Ÿ†•
  • Load from Apache Kafka
  • Load from Apache Hadoop
  • Querying data
  • Roll-up
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  • Updating existing data
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  • Writing an ingestion spec
  • Transforming input data
  • Tutorial: Run with Docker
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Design

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Ingestion

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  • Stream ingestion

    • Apache Kafka ingestion
    • Apache Kafka supervisor
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    Batch ingestion

    • Native batch
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    SQL-based ingestion ๐Ÿ†•

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Querying

    Druid SQL

    • Overview and syntax
    • SQL data types
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    • Scalar functions
    • Aggregation functions
    • Multi-value string functions
    • JSON functions
    • All functions
    • Druid SQL API
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    • Datasources
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    • Multi-value dimensions
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    • Using query caching
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    Native query types

    • Timeseries
    • TopN
    • GroupBy
    • Scan
    • Search
    • TimeBoundary
    • SegmentMetadata
    • DatasourceMetadata

    Native query components

    • Filters
    • Granularities
    • Dimensions
    • Aggregations
    • Post-aggregations
    • Expressions
    • Having filters (groupBy)
    • Sorting and limiting (groupBy)
    • Sorting (topN)
    • String comparators
    • Virtual columns
    • Spatial filters

Configuration

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Operations

  • Web console
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    Performance tuning

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    • HTTP compression
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    Monitoring

    • Request logging
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    • Alerts
  • API reference
  • High availability
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  • Using rules to drop and retain data
  • Working with different versions of Apache Hadoop
  • Misc

    • dump-segment tool
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Development

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Misc

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Hidden

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  • Authentication and Authorization
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  • Select
  • Firehose (deprecated)
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Edit

SQL JSON functions

Druid supports nested columns, which provide optimized storage and indexes for nested data structures. See Nested columns for more information.

You can use the following JSON functions to extract, transform, and create COMPLEX<json> values.

FunctionNotes
JSON_KEYS(expr, path)Returns an array of field names from expr at the specified path.
JSON_OBJECT(KEY expr1 VALUE expr2[, KEY expr3 VALUE expr4, ...])Constructs a new COMPLEX<json> object. The KEY expressions must evaluate to string types. The VALUE expressions can be composed of any input type, including other COMPLEX<json> values. JSON_OBJECT can accept colon-separated key-value pairs. The following syntax is equivalent: JSON_OBJECT(expr1:expr2[, expr3:expr4, ...]).
JSON_PATHS(expr)Returns an array of all paths which refer to literal values in expr in JSONPath format.
JSON_QUERY(expr, path)Extracts a COMPLEX<json> value from expr, at the specified path.
JSON_VALUE(expr, path [RETURNING sqlType])Extracts a literal value from expr at the specified path. If you specify RETURNING and an SQL type name (such as VARCHAR, BIGINT, DOUBLE, etc) the function plans the query using the suggested type. Otherwise, it attempts to infer the type based on the context. If it can't infer the type, it defaults to VARCHAR.
PARSE_JSON(expr)Parses expr into a COMPLEX<json> object. This operator deserializes JSON values when processing them, translating stringified JSON into a nested structure. If the input is not a VARCHAR or it is invalid JSON, this function will result in an error.
TRY_PARSE_JSON(expr)Parses expr into a COMPLEX<json> object. This operator deserializes JSON values when processing them, translating stringified JSON into a nested structure. If the input is not a VARCHAR or it is invalid JSON, this function will result in a NULL value.
TO_JSON_STRING(expr)Serializes expr into a JSON string.

JSONPath syntax

Druid supports a subset of the JSONPath syntax operators, primarily limited to extracting individual values from nested data structures.

OperatorDescription
$Root element. All JSONPath expressions start with this operator.
.<name>Child element in dot notation.
['<name>']Child element in bracket notation.
[<number>]Array index.

Consider the following example input JSON:

{"x":1, "y":[1, 2, 3]}
  • To return the entire JSON object:
    $ -> {"x":1, "y":[1, 2, 3]}
  • To return the value of the key "x":
    $.x -> 1
  • For a key that contains an array, to return the entire array:
    $['y'] -> [1, 2, 3]
  • For a key that contains an array, to return an item in the array:
    $.y[1] -> 2
โ† Multi-value string functionsAll functions โ†’

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