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:

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

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:

Result:

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

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:

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

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:

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

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:

Result:

simpleJSONExtractBool

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

Syntax

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:

Result:

simpleJSONExtractRaw

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

Syntax

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:

Result:

simpleJSONExtractString

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

Syntax

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

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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

Examples

JSONHas

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

Syntax

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:

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:

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

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

JSONType

Return the type of a JSON value. If the value does not exist, Null=0 will be returned (not usual Null, but Null=0 of Enum8('Null' = 0, 'String' = 34,...). .

Syntax

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=0. Enum.

Examples

JSONExtractUInt

Parses JSON and extracts a value of UInt type.

Syntax

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 0. UInt64.

Examples

Query:

Result:

JSONExtractInt

Parses JSON and extracts a value of Int type.

Syntax

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 0. Int64.

Examples

Query:

Result:

JSONExtractFloat

Parses JSON and extracts a value of Int type.

Syntax

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 0. Float64.

Examples

Query:

Result:

JSONExtractBool

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

Syntax

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

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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

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

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

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

Referring to a nested values by passing multiple indices_or_keys parameters:

Result:

JSONExtractKeysAndValues

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

Syntax

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

JSONExtractKeys

Parses a JSON string and extracts the keys.

Syntax

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

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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

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

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

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

JSONExtractKeysAndValuesRaw

Extracts raw data from a JSON object.

Syntax

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

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Result:

Query:

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Query:

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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

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

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

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

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Result:

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

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

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Result:

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

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:

Result:

See Also

• output_format_json_quote_64bit_integers
• output_format_json_quote_denormals

JSONArrayLength

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

Syntax

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

jsonMergePatch

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

Syntax

Arguments

• json — String with valid JSON.

Returned value

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

Example

JSONAllPaths

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

Syntax

Arguments

• json — JSON.

Returned value

• An array of paths. Array(String).

Example

JSONAllPathsWithTypes

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

Syntax

Arguments

• json — JSON.

Returned value

• An array of paths. Map(String, String).

Example

JSONDynamicPaths

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

Syntax

Arguments

• json — JSON.

Returned value

• An array of paths. Array(String).

Example

JSONDynamicPathsWithTypes

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

Syntax

Arguments

• json — JSON.

Returned value

• An array of paths. Map(String, String).

Example

JSONSharedDataPaths

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

Syntax

Arguments

• json — JSON.

Returned value

• An array of paths. Array(String).

Example

JSONSharedDataPathsWithTypes

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

Syntax

Arguments

• json — JSON.

Returned value

• An array of paths. Map(String, String).

Example