ClickHouse/docs/en/sql-reference/functions/json-functions.md

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56	JSON

Functions for Working with JSON

In Yandex.Metrica, JSON is transmitted by users as session parameters. There are some special functions for working with this JSON. (Although in most of the cases, the JSONs are additionally pre-processed, and the resulting values are put in separate columns in their processed format.) All these 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: visitParamHas('{"abc":"def"}', 'abc') = 1, but visitParamHas('{"\\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.

visitParamHas(params, name)

Checks whether there is a field with the name name.

Alias: simpleJSONHas.

visitParamExtractUInt(params, name)

Parses UInt64 from the value of the field named 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.

Alias: simpleJSONExtractUInt.

visitParamExtractInt(params, name)

The same as for Int64.

Alias: simpleJSONExtractInt.

visitParamExtractFloat(params, name)

The same as for Float64.

Alias: simpleJSONExtractFloat.

visitParamExtractBool(params, name)

Parses a true/false value. The result is UInt8.

Alias: simpleJSONExtractBool.

visitParamExtractRaw(params, name)

Returns the value of a field, including separators.

Alias: simpleJSONExtractRaw.

Examples:

visitParamExtractRaw('{"abc":"\\n\\u0000"}', 'abc') = '"\\n\\u0000"';
visitParamExtractRaw('{"abc":{"def":[1,2,3]}}', 'abc') = '{"def":[1,2,3]}';

visitParamExtractString(params, name)

Parses the string in double quotes. The value is unescaped. If unescaping failed, it returns an empty string.

Alias: simpleJSONExtractString.

Examples:

visitParamExtractString('{"abc":"\\n\\u0000"}', 'abc') = '\n\0';
visitParamExtractString('{"abc":"\\u263a"}', 'abc') = '☺';
visitParamExtractString('{"abc":"\\u263"}', 'abc') = '';
visitParamExtractString('{"abc":"hello}', 'abc') = '';

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).

The following functions are based on simdjson designed for more complex JSON parsing requirements. The assumption 2 mentioned above still applies.

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": [-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 "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 "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.

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'));

Result:

"world"
0
2
String

!!! note "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

• output_format_json_quote_64bit_integers
• output_format_json_quote_denormals