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json-functions

There are two sets of functions to parse JSON.

  • simpleJSON* (visitParam*) is made to parse a special very limited subset of a JSON, but these functions are extremely fast.
  • JSONExtract* is made to parse normal 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, but they try to do as little as possible to get the job done.

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)

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 field exists, 0 otherwise.

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;
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)

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

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;
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)

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

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;
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)

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

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;
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)

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;
0
1
0
0

simpleJSONExtractRaw​

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

Syntax

simpleJSONExtractRaw(json, field_name)

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

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;

"-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)

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 the value of a field as a String, including separators. The value is unescaped. It returns an empty String: if the field doesn't contain a double quoted string, if unescaping fails or if the field doesn't exist.

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;
\n\0

☺

visitParamHas​

This function is an alias of simpleJSONHas.

visitParamExtractUInt​

This function is an alias of simpleJSONExtractUInt.

visitParamExtractInt​

This function is an alias of simpleJSONExtractInt.

visitParamExtractFloat​

This function is an alias of simpleJSONExtractFloat.

visitParamExtractBool​

This function is an alias of simpleJSONExtractBool.

visitParamExtractRaw​

This function is an alias of simpleJSONExtractRaw.

visitParamExtractString​

This function is an alias of simpleJSONExtractString.

JSONExtract functions

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

isValidJSON(json)​

Checks that passed string is a valid json.

Examples:

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

JSONHas(json[, indices_or_keys]…)​

If the value exists in the JSON document, 1 will be returned.

If the value does not exist, 0 will be returned.

Examples:

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

indices_or_keys is a list of zero or more arguments each of them can be either string or integer.

  • 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.

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.

So, 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(json[, indices_or_keys]…)​

Return the length of a JSON array or a JSON object.

If the value does not exist or has a wrong type, 0 will be returned.

Examples:

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

JSONType(json[, indices_or_keys]…)​

Return the type of a JSON value.

If the value does not exist, Null will be returned.

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(json[, indices_or_keys]…)​

JSONExtractInt(json[, indices_or_keys]…)​

JSONExtractFloat(json[, indices_or_keys]…)​

JSONExtractBool(json[, indices_or_keys]…)​

Parses a JSON and extract a value. These functions are similar to visitParam functions.

If the value does not exist or has a wrong type, 0 will be returned.

Examples:

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

JSONExtractString(json[, indices_or_keys]…)​

Parses a JSON and extract 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.

The value is unescaped. If unescaping failed, it returns an empty 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(json[, indices_or_keys…], Return_type)​

Parses a JSON and extract a value of the given ClickHouse data type.

This is a generalization of the previous JSONExtract<type> functions. This means JSONExtract(..., 'String') returns exactly the same as JSONExtractString(), JSONExtract(..., 'Float64') returns exactly the same as JSONExtractFloat().

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(json[, indices_or_keys…], Value_type)​

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

Arguments

  • 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

Array with the keys of the JSON.

Type: 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(json[, indices_or_keys]…)​

Returns a part of JSON as unparsed string.

If the part does not exist or has a wrong type, an empty string will be returned.

Example:

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

JSONExtractArrayRaw(json[, indices_or_keys…])​

Returns an array with elements of JSON array, each represented as unparsed string.

If the part does not exist or isn’t array, an empty array will be returned.

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.
  • Empty array if the requested object does not exist, or input JSON is invalid.

Type: 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(json, path)​

If the value exists in the JSON document, 1 will be returned.

If the value does not exist, 0 will be returned.

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]');
note

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

JSON_QUERY(json, path)​

Parses a JSON and extract a value as JSON array or JSON object.

If the value does not exist, an empty string will be returned.

Example:

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
note

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

JSON_VALUE(json, path)​

Parses a JSON and extract a value as JSON scalar.

If the value does not exist, an empty string will be returned by default, and 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, and by SET function_json_value_return_type_allow_complex = true, the complex value will be returned.

Example:

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
note

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

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.

Type: 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.

Type: 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.

Type: String.

Example

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

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