Relational Data - Functions - Json Functions

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There are two sets of functions to parse JSON: - simpleJSON* (visitParam*) which is made for parsing a limited subset of JSON extremely fast. - JSONExtract* which is made for parsing ordinary JSON.

simpleJSON (visitParam) functions

ClickHouse has special functions for working with simplified JSON. All these JSON functions are based on strong assumptions about what the JSON can be. They try to do as little as possible to get the job done as quickly as possible.

The following assumptions are made:

  1. The field name (function argument) must be a constant.
  2. The field name is somehow canonically encoded in JSON. For example: simpleJSONHas('{"abc":"def"}', 'abc') = 1, but simpleJSONHas('{"\\u0061\\u0062\\u0063":"def"}', 'abc') = 0
  3. Fields are searched for on any nesting level, indiscriminately. If there are multiple matching fields, the first occurrence is used.
  4. The JSON does not have space characters outside of string literals.

simpleJSONHas

Checks whether there is a field named field_name. The result is UInt8.

Syntax 

simpleJSONHas(json, field_name)

Alias: visitParamHas.

Parameters

  • json — The JSON in which the field is searched for. String
  • field_name — The name of the field to search for. String literal

Returned value

  • Returns 1 if the field exists, 0 otherwise. UInt8.

Example

Query: 

CREATE TABLE jsons
(
    `json` String
)
ENGINE = Memory;

INSERT INTO jsons VALUES ('{"foo":"true","qux":1}');

SELECT simpleJSONHas(json, 'foo') FROM jsons;
SELECT simpleJSONHas(json, 'bar') FROM jsons;

Result: 

1
0

simpleJSONExtractUInt

Parses UInt64 from the value of the field named field_name. If this is a string field, it tries to parse a number from the beginning of the string. If the field does not exist, or it exists but does not contain a number, it returns 0.

Syntax 

simpleJSONExtractUInt(json, field_name)

Alias: visitParamExtractUInt.

Parameters

  • json — The JSON in which the field is searched for. String
  • field_name — The name of the field to search for. String literal

Returned value

  • Returns the number parsed from the field if the field exists and contains a number, 0 otherwise. UInt64.

Example

Query: 

CREATE TABLE jsons
(
    `json` String
)
ENGINE = Memory;

INSERT INTO jsons VALUES ('{"foo":"4e3"}');
INSERT INTO jsons VALUES ('{"foo":3.4}');
INSERT INTO jsons VALUES ('{"foo":5}');
INSERT INTO jsons VALUES ('{"foo":"not1number"}');
INSERT INTO jsons VALUES ('{"baz":2}');

SELECT simpleJSONExtractUInt(json, 'foo') FROM jsons ORDER BY json;

Result: 

0
4
0
3
5

simpleJSONExtractInt

Parses Int64 from the value of the field named field_name. If this is a string field, it tries to parse a number from the beginning of the string. If the field does not exist, or it exists but does not contain a number, it returns 0.

Syntax 

simpleJSONExtractInt(json, field_name)

Alias: visitParamExtractInt.

Parameters

  • json — The JSON in which the field is searched for. String
  • field_name — The name of the field to search for. String literal

Returned value

  • Returns the number parsed from the field if the field exists and contains a number, 0 otherwise. Int64.

Example

Query: 

CREATE TABLE jsons
(
    `json` String
)
ENGINE = Memory;

INSERT INTO jsons VALUES ('{"foo":"-4e3"}');
INSERT INTO jsons VALUES ('{"foo":-3.4}');
INSERT INTO jsons VALUES ('{"foo":5}');
INSERT INTO jsons VALUES ('{"foo":"not1number"}');
INSERT INTO jsons VALUES ('{"baz":2}');

SELECT simpleJSONExtractInt(json, 'foo') FROM jsons ORDER BY json;

Result: 

0
-4
0
-3
5

simpleJSONExtractFloat

Parses Float64 from the value of the field named field_name. If this is a string field, it tries to parse a number from the beginning of the string. If the field does not exist, or it exists but does not contain a number, it returns 0.

Syntax 

simpleJSONExtractFloat(json, field_name)

Alias: visitParamExtractFloat.

Parameters

  • json — The JSON in which the field is searched for. String
  • field_name — The name of the field to search for. String literal

Returned value

  • Returns the number parsed from the field if the field exists and contains a number, 0 otherwise. Float64.

Example

Query: 

CREATE TABLE jsons
(
    `json` String
)
ENGINE = Memory;

INSERT INTO jsons VALUES ('{"foo":"-4e3"}');
INSERT INTO jsons VALUES ('{"foo":-3.4}');
INSERT INTO jsons VALUES ('{"foo":5}');
INSERT INTO jsons VALUES ('{"foo":"not1number"}');
INSERT INTO jsons VALUES ('{"baz":2}');

SELECT simpleJSONExtractFloat(json, 'foo') FROM jsons ORDER BY json;

Result: 

0
-4000
0
-3.4
5

simpleJSONExtractBool

Parses a true/false value from the value of the field named field_name. The result is UInt8.

Syntax 

simpleJSONExtractBool(json, field_name)

Alias: visitParamExtractBool.

Parameters

  • json — The JSON in which the field is searched for. String
  • field_name — The name of the field to search for. String literal

Returned value

It returns 1 if the value of the field is true, 0 otherwise. This means this function will return 0 including (and not only) in the following cases: - If the field doesn’t exists. - If the field contains true as a string, e.g.: {"field":"true"}. - If the field contains 1 as a numerical value.

Example

Query: 

CREATE TABLE jsons
(
    `json` String
)
ENGINE = Memory;

INSERT INTO jsons VALUES ('{"foo":false,"bar":true}');
INSERT INTO jsons VALUES ('{"foo":"true","qux":1}');

SELECT simpleJSONExtractBool(json, 'bar') FROM jsons ORDER BY json;
SELECT simpleJSONExtractBool(json, 'foo') FROM jsons ORDER BY json;

Result: 

0
1
0
0

simpleJSONExtractRaw

Returns the value of the field named field_name as a String, including separators.

Syntax 

simpleJSONExtractRaw(json, field_name)

Alias: visitParamExtractRaw.

Parameters

  • json — The JSON in which the field is searched for. String
  • field_name — The name of the field to search for. String literal

Returned value

  • Returns the value of the field as a string, including separators if the field exists, or an empty string otherwise. String

Example

Query: 

CREATE TABLE jsons
(
    `json` String
)
ENGINE = Memory;

INSERT INTO jsons VALUES ('{"foo":"-4e3"}');
INSERT INTO jsons VALUES ('{"foo":-3.4}');
INSERT INTO jsons VALUES ('{"foo":5}');
INSERT INTO jsons VALUES ('{"foo":{"def":[1,2,3]}}');
INSERT INTO jsons VALUES ('{"baz":2}');

SELECT simpleJSONExtractRaw(json, 'foo') FROM jsons ORDER BY json;

Result: 

"-4e3"
-3.4
5
{"def":[1,2,3]}

simpleJSONExtractString

Parses String in double quotes from the value of the field named field_name.

Syntax 

simpleJSONExtractString(json, field_name)

Alias: visitParamExtractString.

Parameters

  • json — The JSON in which the field is searched for. String
  • field_name — The name of the field to search for. String literal

Returned value

  • Returns the unescaped value of a field as a string, including separators. An empty string is returned if the field doesn’t contain a double quoted string, if unescaping fails or if the field doesn’t exist. String.

Implementation details

There is currently no support for code points in the format \uXXXX\uYYYY that are not from the basic multilingual plane (they are converted to CESU-8 instead of UTF-8).

Example

Query: 

CREATE TABLE jsons
(
    `json` String
)
ENGINE = Memory;

INSERT INTO jsons VALUES ('{"foo":"\\n\\u0000"}');
INSERT INTO jsons VALUES ('{"foo":"\\u263"}');
INSERT INTO jsons VALUES ('{"foo":"\\u263a"}');
INSERT INTO jsons VALUES ('{"foo":"hello}');

SELECT simpleJSONExtractString(json, 'foo') FROM jsons ORDER BY json;

Result: 

\n\0

☺

JSONExtract functions

The following functions are based on simdjson, and designed for more complex JSON parsing requirements.

isValidJSON

Checks that passed string is valid JSON.

Syntax 

isValidJSON(json)

Examples 

SELECT isValidJSON('{"a": "hello", "b": [-100, 200.0, 300]}') = 1
SELECT isValidJSON('not a json') = 0

JSONHas

If the value exists in the JSON document, 1 will be returned. If the value does not exist, 0 will be returned.

Syntax 

JSONHas(json [, indices_or_keys]...)

Parameters

  • json — JSON string to parse. String.
  • indices_or_keys — A list of zero or more arguments, each of which can be either string or integer. String, Int*.

indices_or_keys type: - String = access object member by key. - Positive integer = access the n-th member/key from the beginning. - Negative integer = access the n-th member/key from the end.

Returned value

  • Returns 1 if the value exists in json, otherwise 0. UInt8.

Examples

Query: 

SELECT JSONHas('{"a": "hello", "b": [-100, 200.0, 300]}', 'b') = 1
SELECT JSONHas('{"a": "hello", "b": [-100, 200.0, 300]}', 'b', 4) = 0

The minimum index of the element is 1. Thus the element 0 does not exist. You may use integers to access both JSON arrays and JSON objects. For example: 

SELECT JSONExtractKey('{"a": "hello", "b": [-100, 200.0, 300]}', 1) = 'a'
SELECT JSONExtractKey('{"a": "hello", "b": [-100, 200.0, 300]}', 2) = 'b'
SELECT JSONExtractKey('{"a": "hello", "b": [-100, 200.0, 300]}', -1) = 'b'
SELECT JSONExtractKey('{"a": "hello", "b": [-100, 200.0, 300]}', -2) = 'a'
SELECT JSONExtractString('{"a": "hello", "b": [-100, 200.0, 300]}', 1) = 'hello'

JSONLength

Return the length of a JSON array or a JSON object. If the value does not exist or has the wrong type, 0 will be returned.

Syntax 

JSONLength(json [, indices_or_keys]...)

Parameters

  • json — JSON string to parse. String.
  • indices_or_keys — A list of zero or more arguments, each of which can be either string or integer. String, Int*.

indices_or_keys type: - String = access object member by key. - Positive integer = access the n-th member/key from the beginning. - Negative integer = access the n-th member/key from the end.

Returned value

  • Returns the length of the JSON array or JSON object. Returns 0 if the value does not exist or has the wrong type. UInt64.

Examples 

SELECT JSONLength('{"a": "hello", "b": [-100, 200.0, 300]}', 'b') = 3
SELECT JSONLength('{"a": "hello", "b": [-100, 200.0, 300]}') = 2

JSONType

Return the type of a JSON value. If the value does not exist, Null will be returned.

Syntax 

JSONType(json [, indices_or_keys]...)

Parameters

  • json — JSON string to parse. String.
  • indices_or_keys — A list of zero or more arguments, each of which can be either string or integer. String, Int*.

indices_or_keys type: - String = access object member by key. - Positive integer = access the n-th member/key from the beginning. - Negative integer = access the n-th member/key from the end.

Returned value

  • Returns the type of a JSON value as a string, otherwise if the value doesn’t exists it returns Null. String.

Examples 

SELECT JSONType('{"a": "hello", "b": [-100, 200.0, 300]}') = 'Object'
SELECT JSONType('{"a": "hello", "b": [-100, 200.0, 300]}', 'a') = 'String'
SELECT JSONType('{"a": "hello", "b": [-100, 200.0, 300]}', 'b') = 'Array'

JSONExtractUInt

Parses JSON and extracts a value of UInt type.

Syntax 

JSONExtractUInt(json [, indices_or_keys]...)

Parameters

  • json — JSON string to parse. String.
  • indices_or_keys — A list of zero or more arguments, each of which can be either string or integer. String, Int*.

indices_or_keys type: - String = access object member by key. - Positive integer = access the n-th member/key from the beginning. - Negative integer = access the n-th member/key from the end.

Returned value

  • Returns a UInt value if it exists, otherwise it returns Null. UInt64.

Examples

Query: 

SELECT JSONExtractUInt('{"a": "hello", "b": [-100, 200.0, 300]}', 'b', -1) as x, toTypeName(x);

Result: 

┌───x─┬─toTypeName(x)─┐
│ 300 │ UInt64        │
└─────┴───────────────┘

JSONExtractInt

Parses JSON and extracts a value of Int type.

Syntax 

JSONExtractInt(json [, indices_or_keys]...)

Parameters

  • json — JSON string to parse. String.
  • indices_or_keys — A list of zero or more arguments, each of which can be either string or integer. String, Int*.

indices_or_keys type: - String = access object member by key. - Positive integer = access the n-th member/key from the beginning. - Negative integer = access the n-th member/key from the end.

Returned value

  • Returns an Int value if it exists, otherwise it returns Null. Int64.

Examples

Query: 

SELECT JSONExtractInt('{"a": "hello", "b": [-100, 200.0, 300]}', 'b', -1) as x, toTypeName(x);

Result: 

┌───x─┬─toTypeName(x)─┐
│ 300 │ Int64         │
└─────┴───────────────┘

JSONExtractFloat

Parses JSON and extracts a value of Int type.

Syntax 

JSONExtractFloat(json [, indices_or_keys]...)

Parameters

  • json — JSON string to parse. String.
  • indices_or_keys — A list of zero or more arguments, each of which can be either string or integer. String, Int*.

indices_or_keys type: - String = access object member by key. - Positive integer = access the n-th member/key from the beginning. - Negative integer = access the n-th member/key from the end.

Returned value

  • Returns an Float value if it exists, otherwise it returns Null. Float64.

Examples

Query: 

SELECT JSONExtractFloat('{"a": "hello", "b": [-100, 200.0, 300]}', 'b', 2) as x, toTypeName(x);

Result: 

┌───x─┬─toTypeName(x)─┐
│ 200 │ Float64       │
└─────┴───────────────┘

JSONExtractBool

Parses JSON and extracts a boolean value. If the value does not exist or has a wrong type, 0 will be returned.

Syntax 

JSONExtractBool(json\[, indices_or_keys\]...)

Parameters

  • json — JSON string to parse. String.
  • indices_or_keys — A list of zero or more arguments, each of which can be either string or integer. String, Int*.

indices_or_keys type: - String = access object member by key. - Positive integer = access the n-th member/key from the beginning. - Negative integer = access the n-th member/key from the end.

Returned value

  • Returns a Boolean value if it exists, otherwise it returns 0. Bool.

Example

Query: 

SELECT JSONExtractBool('{"passed": true}', 'passed');

Result: 

┌─JSONExtractBool('{"passed": true}', 'passed')─┐
│                                             1 │
└───────────────────────────────────────────────┘

JSONExtractString

Parses JSON and extracts a string. This function is similar to visitParamExtractString functions. If the value does not exist or has a wrong type, an empty string will be returned.

Syntax 

JSONExtractString(json [, indices_or_keys]...)

Parameters

  • json — JSON string to parse. String.
  • indices_or_keys — A list of zero or more arguments, each of which can be either string or integer. String, Int*.

indices_or_keys type: - String = access object member by key. - Positive integer = access the n-th member/key from the beginning. - Negative integer = access the n-th member/key from the end.

Returned value

  • Returns an unescaped string from json. If unescaping failed, if the value does not exist or if it has a wrong type then it returns an empty string. String.

Examples 

SELECT JSONExtractString('{"a": "hello", "b": [-100, 200.0, 300]}', 'a') = 'hello'
SELECT JSONExtractString('{"abc":"\\n\\u0000"}', 'abc') = '\n\0'
SELECT JSONExtractString('{"abc":"\\u263a"}', 'abc') = '☺'
SELECT JSONExtractString('{"abc":"\\u263"}', 'abc') = ''
SELECT JSONExtractString('{"abc":"hello}', 'abc') = ''

JSONExtract

Parses JSON and extracts a value of the given ClickHouse data type. This function is a generalized version of the previous JSONExtract<type> functions. Meaning:

JSONExtract(..., 'String') returns exactly the same as JSONExtractString(), JSONExtract(..., 'Float64') returns exactly the same as JSONExtractFloat().

Syntax 

JSONExtract(json [, indices_or_keys...], return_type)

Parameters

  • json — JSON string to parse. String.
  • indices_or_keys — A list of zero or more arguments, each of which can be either string or integer. String, Int*.
  • return_type — A string specifying the type of the value to extract. String.

indices_or_keys type: - String = access object member by key. - Positive integer = access the n-th member/key from the beginning. - Negative integer = access the n-th member/key from the end.

Returned value

  • Returns a value if it exists of the specified return type, otherwise it returns 0, Null, or an empty-string depending on the specified return type. UInt64, Int64, Float64, Bool or String.

Examples 

SELECT JSONExtract('{"a": "hello", "b": [-100, 200.0, 300]}', 'Tuple(String, Array(Float64))') = ('hello',[-100,200,300])
SELECT JSONExtract('{"a": "hello", "b": [-100, 200.0, 300]}', 'Tuple(b Array(Float64), a String)') = ([-100,200,300],'hello')
SELECT JSONExtract('{"a": "hello", "b": "world"}', 'Map(String, String)') = map('a',  'hello', 'b', 'world');
SELECT JSONExtract('{"a": "hello", "b": [-100, 200.0, 300]}', 'b', 'Array(Nullable(Int8))') = [-100, NULL, NULL]
SELECT JSONExtract('{"a": "hello", "b": [-100, 200.0, 300]}', 'b', 4, 'Nullable(Int64)') = NULL
SELECT JSONExtract('{"passed": true}', 'passed', 'UInt8') = 1
SELECT JSONExtract('{"day": "Thursday"}', 'day', 'Enum8(\'Sunday\' = 0, \'Monday\' = 1, \'Tuesday\' = 2, \'Wednesday\' = 3, \'Thursday\' = 4, \'Friday\' = 5, \'Saturday\' = 6)') = 'Thursday'
SELECT JSONExtract('{"day": 5}', 'day', 'Enum8(\'Sunday\' = 0, \'Monday\' = 1, \'Tuesday\' = 2, \'Wednesday\' = 3, \'Thursday\' = 4, \'Friday\' = 5, \'Saturday\' = 6)') = 'Friday'

JSONExtractKeysAndValues

Parses key-value pairs from JSON where the values are of the given ClickHouse data type.

Syntax 

JSONExtractKeysAndValues(json [, indices_or_keys...], value_type)

Parameters

  • json — JSON string to parse. String.
  • indices_or_keys — A list of zero or more arguments, each of which can be either string or integer. String, Int*.
  • value_type — A string specifying the type of the value to extract. String.

indices_or_keys type: - String = access object member by key. - Positive integer = access the n-th member/key from the beginning. - Negative integer = access the n-th member/key from the end.

Returned value

  • Returns an array of parsed key-value pairs. Array(Tuple(value_type)).

Example 

SELECT JSONExtractKeysAndValues('{"x": {"a": 5, "b": 7, "c": 11}}', 'x', 'Int8') = [('a',5),('b',7),('c',11)];

JSONExtractKeys

Parses a JSON string and extracts the keys.

Syntax 

JSONExtractKeys(json[, a, b, c...])

Parameters

  • json — String with valid JSON.
  • a, b, c... — Comma-separated indices or keys that specify the path to the inner field in a nested JSON object. Each argument can be either a String to get the field by the key or an Integer to get the N-th field (indexed from 1, negative integers count from the end). If not set, the whole JSON is parsed as the top-level object. Optional parameter.

Returned value

  • Returns an array with the keys of the JSON. Array(String).

Example

Query: 

SELECT JSONExtractKeys('{"a": "hello", "b": [-100, 200.0, 300]}');

Result: 

text
┌─JSONExtractKeys('{"a": "hello", "b": [-100, 200.0, 300]}')─┐
│ ['a','b']                                                  │
└────────────────────────────────────────────────────────────┘

JSONExtractRaw

Returns part of the JSON as an unparsed string. If the part does not exist or has the wrong type, an empty string will be returned.

Syntax 

JSONExtractRaw(json [, indices_or_keys]...)

Parameters

  • json — JSON string to parse. String.
  • indices_or_keys — A list of zero or more arguments, each of which can be either string or integer. String, Int*.

indices_or_keys type: - String = access object member by key. - Positive integer = access the n-th member/key from the beginning. - Negative integer = access the n-th member/key from the end.

Returned value

  • Returns part of the JSON as an unparsed string. If the part does not exist or has the wrong type, an empty string is returned. String.

Example 

SELECT JSONExtractRaw('{"a": "hello", "b": [-100, 200.0, 300]}', 'b') = '[-100, 200.0, 300]';

JSONExtractArrayRaw

Returns an array with elements of JSON array, each represented as unparsed string. If the part does not exist or isn’t an array, then an empty array will be returned.

Syntax 

JSONExtractArrayRaw(json [, indices_or_keys...])

Parameters

  • json — JSON string to parse. String.
  • indices_or_keys — A list of zero or more arguments, each of which can be either string or integer. String, Int*.

indices_or_keys type: - String = access object member by key. - Positive integer = access the n-th member/key from the beginning. - Negative integer = access the n-th member/key from the end.

Returned value

  • Returns an array with elements of JSON array, each represented as unparsed string. Otherwise, an empty array is returned if the part does not exist or is not an array. Array(String).

Example 

SELECT JSONExtractArrayRaw('{"a": "hello", "b": [-100, 200.0, "hello"]}', 'b') = ['-100', '200.0', '"hello"'];

JSONExtractKeysAndValuesRaw

Extracts raw data from a JSON object.

Syntax 

JSONExtractKeysAndValuesRaw(json[, p, a, t, h])

Arguments

  • json — String with valid JSON.
  • p, a, t, h — Comma-separated indices or keys that specify the path to the inner field in a nested JSON object. Each argument can be either a string to get the field by the key or an integer to get the N-th field (indexed from 1, negative integers count from the end). If not set, the whole JSON is parsed as the top-level object. Optional parameter.

Returned values

Examples

Query: 

SELECT JSONExtractKeysAndValuesRaw('{"a": [-100, 200.0], "b":{"c": {"d": "hello", "f": "world"}}}');

Result: 

┌─JSONExtractKeysAndValuesRaw('{"a": [-100, 200.0], "b":{"c": {"d": "hello", "f": "world"}}}')─┐
│ [('a','[-100,200]'),('b','{"c":{"d":"hello","f":"world"}}')]                                 │
└──────────────────────────────────────────────────────────────────────────────────────────────┘

Query: 

SELECT JSONExtractKeysAndValuesRaw('{"a": [-100, 200.0], "b":{"c": {"d": "hello", "f": "world"}}}', 'b');

Result: 

┌─JSONExtractKeysAndValuesRaw('{"a": [-100, 200.0], "b":{"c": {"d": "hello", "f": "world"}}}', 'b')─┐
│ [('c','{"d":"hello","f":"world"}')]                                                               │
└───────────────────────────────────────────────────────────────────────────────────────────────────┘

Query: 

SELECT JSONExtractKeysAndValuesRaw('{"a": [-100, 200.0], "b":{"c": {"d": "hello", "f": "world"}}}', -1, 'c');

Result: 

┌─JSONExtractKeysAndValuesRaw('{"a": [-100, 200.0], "b":{"c": {"d": "hello", "f": "world"}}}', -1, 'c')─┐
│ [('d','"hello"'),('f','"world"')]                                                                     │
└───────────────────────────────────────────────────────────────────────────────────────────────────────┘

JSON_EXISTS

If the value exists in the JSON document, 1 will be returned. If the value does not exist, 0 will be returned.

Syntax 

JSON_EXISTS(json, path)

Parameters

  • json — A string with valid JSON. String.
  • path — A string representing the path. String.

Before version 21.11 the order of arguments was wrong, i.e. JSON_EXISTS(path, json)


Returned value

  • Returns 1 if the value exists in the JSON document, otherwise 0.

Examples 

SELECT JSON_EXISTS('{"hello":1}', '$.hello');
SELECT JSON_EXISTS('{"hello":{"world":1}}', '$.hello.world');
SELECT JSON_EXISTS('{"hello":["world"]}', '$.hello[*]');
SELECT JSON_EXISTS('{"hello":["world"]}', '$.hello[0]');

JSON_QUERY

Parses a JSON and extract a value as a JSON array or JSON object. If the value does not exist, an empty string will be returned.

Syntax 

JSON_QUERY(json, path)

Parameters

  • json — A string with valid JSON. String.
  • path — A string representing the path. String.

Before version 21.11 the order of arguments was wrong, i.e. JSON_EXISTS(path, json)


Returned value

  • Returns the extracted value as a JSON array or JSON object. Otherwise it returns an empty string if the value does not exist. String.

Example

Query: 

SELECT JSON_QUERY('{"hello":"world"}', '$.hello');
SELECT JSON_QUERY('{"array":[[0, 1, 2, 3, 4, 5], [0, -1, -2, -3, -4, -5]]}', '$.array[*][0 to 2, 4]');
SELECT JSON_QUERY('{"hello":2}', '$.hello');
SELECT toTypeName(JSON_QUERY('{"hello":2}', '$.hello'));

Result: 

["world"]
[0, 1, 4, 0, -1, -4]
[2]
String

JSON_VALUE

Parses a JSON and extract a value as a JSON scalar. If the value does not exist, an empty string will be returned by default.

This function is controlled by the following settings:

  • by SET function_json_value_return_type_allow_nullable = true, NULL will be returned. If the value is complex type (such as: struct, array, map), an empty string will be returned by default.
  • by SET function_json_value_return_type_allow_complex = true, the complex value will be returned.

Syntax 

JSON_VALUE(json, path)

Parameters

  • json — A string with valid JSON. String.
  • path — A string representing the path. String.

Before version 21.11 the order of arguments was wrong, i.e. JSON_EXISTS(path, json)


Returned value

  • Returns the extracted value as a JSON scalar if it exists, otherwise an empty string is returned. String.

Example

Query: 

SELECT JSON_VALUE('{"hello":"world"}', '$.hello');
SELECT JSON_VALUE('{"array":[[0, 1, 2, 3, 4, 5], [0, -1, -2, -3, -4, -5]]}', '$.array[*][0 to 2, 4]');
SELECT JSON_VALUE('{"hello":2}', '$.hello');
SELECT toTypeName(JSON_VALUE('{"hello":2}', '$.hello'));
select JSON_VALUE('{"hello":"world"}', '$.b') settings function_json_value_return_type_allow_nullable=true;
select JSON_VALUE('{"hello":{"world":"!"}}', '$.hello') settings function_json_value_return_type_allow_complex=true;

Result: 

world
0
2
String

toJSONString

Serializes a value to its JSON representation. Various data types and nested structures are supported. 64-bit integers or bigger (like UInt64 or Int128) are enclosed in quotes by default. output_format_json_quote_64bit_integers controls this behavior. Special values NaN and inf are replaced with null. Enable output_format_json_quote_denormals setting to show them. When serializing an Enum value, the function outputs its name.

Syntax 

toJSONString(value)

Arguments

  • value — Value to serialize. Value may be of any data type.

Returned value

  • JSON representation of the value. String.

Example

The first example shows serialization of a Map. The second example shows some special values wrapped into a Tuple.

Query: 

SELECT toJSONString(map('key1', 1, 'key2', 2));
SELECT toJSONString(tuple(1.25, NULL, NaN, +inf, -inf, [])) SETTINGS output_format_json_quote_denormals = 1;

Result: 

{"key1":1,"key2":2}
[1.25,null,"nan","inf","-inf",[]]

See Also

JSONArrayLength

Returns the number of elements in the outermost JSON array. The function returns NULL if input JSON string is invalid.

Syntax 

JSONArrayLength(json)

Alias: JSON_ARRAY_LENGTH(json).

Arguments

  • json — String with valid JSON.

Returned value

  • If json is a valid JSON array string, returns the number of array elements, otherwise returns NULL. Nullable(UInt64).

Example 

SELECT
    JSONArrayLength(''),
    JSONArrayLength('[1,2,3]')

┌─JSONArrayLength('')─┬─JSONArrayLength('[1,2,3]')─┐
│                ᴺᵁᴸᴸ │                          3 │
└─────────────────────┴────────────────────────────┘

jsonMergePatch

Returns the merged JSON object string which is formed by merging multiple JSON objects.

Syntax 

jsonMergePatch(json1, json2, ...)

Arguments

  • json — String with valid JSON.

Returned value

  • If JSON object strings are valid, return the merged JSON object string. String.

Example 

SELECT jsonMergePatch('{"a":1}', '{"name": "joey"}', '{"name": "tom"}', '{"name": "zoey"}') AS res

┌─res───────────────────┐
│ {"a":1,"name":"zoey"} │
└───────────────────────┘

JSONAllPaths

Returns the list of all paths stored in each row in JSON column.

Syntax 

JSONAllPaths(json)

Arguments

Returned value

Example 

CREATE TABLE test (json JSON(max_dynamic_paths=1)) ENGINE = Memory;
INSERT INTO test FORMAT JSONEachRow {"json" : {"a" : 42}}, {"json" : {"b" : "Hello"}}, {"json" : {"a" : [1, 2, 3], "c" : "2020-01-01"}}
SELECT json, JSONAllPaths(json) FROM test;
┌─json─────────────────────────────────┬─JSONAllPaths(json)─┐
│ {"a":"42"}                           │ ['a']              │
│ {"b":"Hello"}                        │ ['b']              │
│ {"a":["1","2","3"],"c":"2020-01-01"} │ ['a','c']          │
└──────────────────────────────────────┴────────────────────┘

JSONAllPathsWithTypes

Returns the map of all paths and their data types stored in each row in JSON column.

Syntax 

JSONAllPathsWithTypes(json)

Arguments

Returned value

Example 

CREATE TABLE test (json JSON(max_dynamic_paths=1)) ENGINE = Memory;
INSERT INTO test FORMAT JSONEachRow {"json" : {"a" : 42}}, {"json" : {"b" : "Hello"}}, {"json" : {"a" : [1, 2, 3], "c" : "2020-01-01"}}
SELECT json, JSONAllPathsWithTypes(json) FROM test;
┌─json─────────────────────────────────┬─JSONAllPathsWithTypes(json)───────────────┐
│ {"a":"42"}                           │ {'a':'Int64'}                             │
│ {"b":"Hello"}                        │ {'b':'String'}                            │
│ {"a":["1","2","3"],"c":"2020-01-01"} │ {'a':'Array(Nullable(Int64))','c':'Date'} │
└──────────────────────────────────────┴───────────────────────────────────────────┘

JSONDynamicPaths

Returns the list of dynamic paths that are stored as separate subcolumns in JSON column.

Syntax 

JSONDynamicPaths(json)

Arguments

Returned value

Example 

CREATE TABLE test (json JSON(max_dynamic_paths=1)) ENGINE = Memory;
INSERT INTO test FORMAT JSONEachRow {"json" : {"a" : 42}}, {"json" : {"b" : "Hello"}}, {"json" : {"a" : [1, 2, 3], "c" : "2020-01-01"}}
SELECT json, JSONDynamicPaths(json) FROM test;
┌─json─────────────────────────────────┬─JSONDynamicPaths(json)─┐
| {"a":"42"}                           │ ['a']                  │
│ {"b":"Hello"}                        │ []                     │
│ {"a":["1","2","3"],"c":"2020-01-01"} │ ['a']                  │
└──────────────────────────────────────┴────────────────────────┘

JSONDynamicPathsWithTypes

Returns the map of dynamic paths that are stored as separate subcolumns and their types in each row in JSON column.

Syntax 

JSONAllPathsWithTypes(json)

Arguments

Returned value

Example 

CREATE TABLE test (json JSON(max_dynamic_paths=1)) ENGINE = Memory;
INSERT INTO test FORMAT JSONEachRow {"json" : {"a" : 42}}, {"json" : {"b" : "Hello"}}, {"json" : {"a" : [1, 2, 3], "c" : "2020-01-01"}}
SELECT json, JSONDynamicPathsWithTypes(json) FROM test;
┌─json─────────────────────────────────┬─JSONDynamicPathsWithTypes(json)─┐
│ {"a":"42"}                           │ {'a':'Int64'}                   │
│ {"b":"Hello"}                        │ {}                              │
│ {"a":["1","2","3"],"c":"2020-01-01"} │ {'a':'Array(Nullable(Int64))'}  │
└──────────────────────────────────────┴─────────────────────────────────┘

JSONSharedDataPaths

Returns the list of paths that are stored in shared data structure in JSON column.

Syntax 

JSONSharedDataPaths(json)

Arguments

Returned value

Example 

CREATE TABLE test (json JSON(max_dynamic_paths=1)) ENGINE = Memory;
INSERT INTO test FORMAT JSONEachRow {"json" : {"a" : 42}}, {"json" : {"b" : "Hello"}}, {"json" : {"a" : [1, 2, 3], "c" : "2020-01-01"}}
SELECT json, JSONSharedDataPaths(json) FROM test;
┌─json─────────────────────────────────┬─JSONSharedDataPaths(json)─┐
│ {"a":"42"}                           │ []                        │
│ {"b":"Hello"}                        │ ['b']                     │
│ {"a":["1","2","3"],"c":"2020-01-01"} │ ['c']                     │
└──────────────────────────────────────┴───────────────────────────┘

JSONSharedDataPathsWithTypes

Returns the map of paths that are stored in shared data structure and their types in each row in JSON column.

Syntax 

JSONSharedDataPathsWithTypes(json)

Arguments

Returned value

Example 

CREATE TABLE test (json JSON(max_dynamic_paths=1)) ENGINE = Memory;
INSERT INTO test FORMAT JSONEachRow {"json" : {"a" : 42}}, {"json" : {"b" : "Hello"}}, {"json" : {"a" : [1, 2, 3], "c" : "2020-01-01"}}
SELECT json, JSONSharedDataPathsWithTypes(json) FROM test;
┌─json─────────────────────────────────┬─JSONSharedDataPathsWithTypes(json)─┐
│ {"a":"42"}                           │ {}                                 │
│ {"b":"Hello"}                        │ {'b':'String'}                     │
│ {"a":["1","2","3"],"c":"2020-01-01"} │ {'c':'Date'}                       │
└──────────────────────────────────────┴────────────────────────────────────┘
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