json-functions

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:

The field name (function argument) must be a constant.
The field name is somehow canonically encoded in JSON. For example: simpleJSONHas('{"abc":"def"}', 'abc') = 1, but simpleJSONHas('{"\\u0061\\u0062\\u0063":"def"}', 'abc') = 0
Fields are searched for on any nesting level, indiscriminately. If there are multiple matching fields, the first occurrence is used.
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:

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:

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:

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:

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

Array with ('key', 'value') tuples. Both tuple members are strings. Array(Tuple(String, String).
Empty array if the requested object does not exist, or input JSON is invalid. Array(Tuple(String, String).

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.

note

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.

note

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.

note

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"} │
└───────────────────────┘

simpleJSON (visitParam) functions​

simpleJSONHas​

simpleJSONExtractUInt​

simpleJSONExtractInt​

simpleJSONExtractFloat​

simpleJSONExtractBool​

simpleJSONExtractRaw​

simpleJSONExtractString​

JSONExtract functions​

isValidJSON​

JSONHas​

JSONLength​

JSONType​

JSONExtractUInt​

JSONExtractInt​

JSONExtractFloat​

JSONExtractBool​

JSONExtractString​

JSONExtract​

JSONExtractKeysAndValues​

JSONExtractKeys​

JSONExtractRaw​

JSONExtractArrayRaw​

JSONExtractKeysAndValuesRaw​

JSON_EXISTS​

JSON_QUERY​

JSON_VALUE​

toJSONString​

JSONArrayLength​

jsonMergePatch​

simpleJSON (visitParam) functions

simpleJSONHas

simpleJSONExtractUInt

simpleJSONExtractInt

simpleJSONExtractFloat

simpleJSONExtractBool

simpleJSONExtractRaw

simpleJSONExtractString

JSONExtract functions

isValidJSON

JSONHas

JSONLength

JSONType

JSONExtractUInt

JSONExtractInt

JSONExtractFloat

JSONExtractBool

JSONExtractString

JSONExtract

JSONExtractKeysAndValues

JSONExtractKeys

JSONExtractRaw

JSONExtractArrayRaw

JSONExtractKeysAndValuesRaw

JSON_EXISTS

JSON_QUERY

JSON_VALUE

toJSONString

JSONArrayLength

jsonMergePatch