JSON Functions and Operators¶

Cast to JSON¶

Casting from BOOLEAN, TINYINT, SMALLINT, INTEGER, BIGINT, REAL, DOUBLE or VARCHAR is supported. Casting from ARRAY, MAP or ROW is supported when the element type of the array is one of the supported types, or when the key type of the map is VARCHAR and value type of the map is one of the supported types, or when every field type of the row is one of the supported types. Behaviors of the casts are shown with the examples below:

SELECT CAST(NULL AS JSON); -- NULL
SELECT CAST(1 AS JSON); -- JSON '1'
SELECT CAST(9223372036854775807 AS JSON); -- JSON '9223372036854775807'
SELECT CAST('abc' AS JSON); -- JSON '"abc"'
SELECT CAST(true AS JSON); -- JSON 'true'
SELECT CAST(1.234 AS JSON); -- JSON '1.234'
SELECT CAST(ARRAY[1, 23, 456] AS JSON); -- JSON '[1,23,456]'
SELECT CAST(ARRAY[1, NULL, 456] AS JSON); -- JSON '[1,null,456]'
SELECT CAST(ARRAY[ARRAY[1, 23], ARRAY[456]] AS JSON); -- JSON '[[1,23],[456]]'
SELECT CAST(MAP_FROM_ENTRIES(ARRAY[('k1', 1), ('k2', 23), ('k3', 456)]) AS JSON); -- JSON '{"k1":1,"k2":23,"k3":456}'
SELECT CAST(CAST(ROW(123, 'abc', true) AS ROW(v1 BIGINT, v2 VARCHAR, v3 BOOLEAN)) AS JSON); -- JSON '[123,"abc",true]'

Note

Casting from NULL to JSON is not straightforward. Casting from a standalone NULL will produce a SQL NULL instead of JSON 'null'. However, when casting from arrays or map containing NULLs, the produced JSON will have nulls in it.

Note

When casting from ROW to JSON, the result is a JSON array rather than a JSON object. This is because positions are more important than names for rows in SQL.

Note

Set the session property field_names_in_json_cast_enabled to true to preserve the row field names as JSON field names. With field_names_in_json_cast_enabled=false, the result of:

SELECT CAST(CAST(ROW(123, 'abc', true) AS ROW(v1 BIGINT, v2 VARCHAR, v3 BOOLEAN)) AS JSON);

is:

JSON '[123,"abc",true]'

With field_names_in_json_cast_enabled=true, the result is:

JSON '{"v1":123,"v2":"abc","v3":true}'

Cast from JSON¶

Casting to BOOLEAN, TINYINT, SMALLINT, INTEGER, BIGINT, REAL, DOUBLE or VARCHAR is supported. Casting to ARRAY and MAP is supported when the element type of the array is one of the supported types, or when the key type of the map is VARCHAR and value type of the map is one of the supported types. Behaviors of the casts are shown with the examples below:

SELECT CAST(JSON 'null' AS VARCHAR); -- NULL
SELECT CAST(JSON '1' AS INTEGER); -- 1
SELECT CAST(JSON '9223372036854775807' AS BIGINT); -- 9223372036854775807
SELECT CAST(JSON '"abc"' AS VARCHAR); -- abc
SELECT CAST(JSON 'true' AS BOOLEAN); -- true
SELECT CAST(JSON '1.234' AS DOUBLE); -- 1.234
SELECT CAST(JSON '[1,23,456]' AS ARRAY(INTEGER)); -- [1, 23, 456]
SELECT CAST(JSON '[1,null,456]' AS ARRAY(INTEGER)); -- [1, NULL, 456]
SELECT CAST(JSON '[[1,23],[456]]' AS ARRAY(ARRAY(INTEGER))); -- [[1, 23], [456]]
SELECT CAST(JSON '{"k1":1,"k2":23,"k3":456}' AS MAP(VARCHAR, INTEGER)); -- {k1=1, k2=23, k3=456}
SELECT CAST(JSON '{"v1":123,"v2":"abc","v3":true}' AS ROW(v1 BIGINT, v2 VARCHAR, v3 BOOLEAN)); -- {v1=123, v2=abc, v3=true}
SELECT CAST(JSON '[123,"abc",true]' AS ROW(v1 BIGINT, v2 VARCHAR, v3 BOOLEAN)); -- {v1=123, v2=abc, v3=true}

Note

JSON arrays can have mixed element types and JSON maps can have mixed value types. This makes it impossible to cast them to SQL arrays and maps in some cases. To address this, Presto supports partial casting of arrays and maps:

SELECT CAST(JSON '[[1, 23], 456]' AS ARRAY(JSON)); -- [JSON '[1,23]', JSON '456']
SELECT CAST(JSON '{"k1": [1, 23], "k2": 456}' AS MAP(VARCHAR, JSON)); -- {k1 = JSON '[1,23]', k2 = JSON '456'}
SELECT CAST(JSON '[null]' AS ARRAY(JSON)); -- [JSON 'null']

Note

When casting from JSON to ROW, for legacy support the case of double quoted field names in RowType is ignored when matching. For example:

SELECT CAST(JSON '{"v1":123,"V2":"abc","v3":true}' AS ROW(v1 BIGINT, v2 VARCHAR, v3 BOOLEAN)); -- {v1=123, v2=abc, v3=true}
SELECT CAST(JSON '{"v1":123,"V2":"abc","v3":true}' AS ROW(v1 BIGINT, "V2" VARCHAR, "V3" BOOLEAN)); -- {v1=123, V2=abc, V3=true}

The following statement returns an error due to duplicate field:

SELECT CAST(JSON '{"v1":123,"V2":"abc","v2":"abc2","v3":true}' AS ROW(v1 BIGINT, "V2" VARCHAR, v2 VARCHAR, "V3" BOOLEAN));

To enforce the case of field names in RowType when casting from JSON to ROW, set the configuration property legacy_json_cast to false in the coordinator and the worker’s configuration properties. After setting the property, the matching is case-sensitive for double quoted field names and remains case-insensitive for unquoted field names. For example:

SELECT CAST(JSON '{"v1":123,"V2":"abc","v3":true}' AS ROW(v1 BIGINT, v2 VARCHAR, v3 BOOLEAN)); -- {v1=123, v2=abc, v3=true}
SELECT CAST(JSON '{"v1":123,"V2":"abc","v3":true}' AS ROW(v1 BIGINT, "V2" VARCHAR, v3 BOOLEAN)); -- {v1=123, V2=abc, v3=true}
SELECT CAST(JSON '{"v1":123,"V2":"abc","v3":true}' AS ROW(v1 BIGINT, "v2" VARCHAR, v3 BOOLEAN)); -- {v1=123, v2=null, v3=true}
SELECT CAST(JSON '{"v1":123,"V2":"abc", "v2":"abc2","v3":true}' AS ROW(v1 BIGINT, v2 VARCHAR, "V2" VARCHAR, v3 BOOLEAN)); -- {v1=123, v2=abc2, V2=abc, v3=true}

If the name of a field does not match (including case sensitivity), the value is null.

Note

When casting from JSON to ROW, both JSON array and JSON object are supported.

JSON Functions¶

is_json_scalar(json) -> boolean()¶

Determine if json is a scalar (i.e. a JSON number, a JSON string, true, false or null):

SELECT is_json_scalar('1'); -- true
SELECT is_json_scalar('[1, 2, 3]'); -- false

json_array_contains(json, value) -> boolean()¶

Determine if value exists in json (a string containing a JSON array):

SELECT json_array_contains('[1, 2, 3]', 2);

json_array_get(json_array, index) -> json()¶

Warning

The semantics of this function are broken. If the extracted element is a string, it will be converted into an invalid JSON value that is not properly quoted (the value will not be surrounded by quotes and any interior quotes will not be escaped).

We recommend against using this function. It cannot be fixed without impacting existing usages and may be removed in a future release.

Returns the element at the specified index into the json_array. The index is zero-based:

SELECT json_array_get('["a", [3, 9], "c"]', 0); -- JSON 'a' (invalid JSON)
SELECT json_array_get('["a", [3, 9], "c"]', 1); -- JSON '[3,9]'

This function also supports negative indexes for fetching element indexed from the end of an array:

SELECT json_array_get('["c", [3, 9], "a"]', -1); -- JSON 'a' (invalid JSON)
SELECT json_array_get('["c", [3, 9], "a"]', -2); -- JSON '[3,9]'

If the element at the specified index doesn’t exist, the function returns null:

SELECT json_array_get('[]', 0); -- null
SELECT json_array_get('["a", "b", "c"]', 10); -- null
SELECT json_array_get('["c", "b", "a"]', -10); -- null

json_array_length(json) -> bigint()¶

Returns the array length of json (a string containing a JSON array):

SELECT json_array_length('[1, 2, 3]');

json_extract(json, json_path) -> json()¶

Evaluates the JSONPath-like expression json_path on json (a string containing JSON) and returns the result as a JSON string:

SELECT json_extract(json, '$.store.book');

json_extract_scalar(json, json_path) -> varchar()¶

Like json_extract(), but returns the result value as a string (as opposed to being encoded as JSON). The value referenced by json_path must be a scalar (boolean, number or string):

SELECT json_extract_scalar('[1, 2, 3]', '$[2]');
SELECT json_extract_scalar(json, '$.store.book[0].author');

json_format(json) -> varchar()¶

Returns the JSON text serialized from the input JSON value. This is inverse function to json_parse():

SELECT json_format(JSON '[1, 2, 3]'); -- '[1,2,3]'
SELECT json_format(JSON '"a"'); -- '"a"'

Note

json_format() and CAST(json AS VARCHAR) have completely different semantics.

json_format() serializes the input JSON value to JSON text conforming to RFC 7159. The JSON value can be a JSON object, a JSON array, a JSON string, a JSON number, true, false or null:

SELECT json_format(JSON '{"a": 1, "b": 2}'); -- '{"a":1,"b":2}'
SELECT json_format(JSON '[1, 2, 3]'); -- '[1,2,3]'
SELECT json_format(JSON '"abc"'); -- '"abc"'
SELECT json_format(JSON '42'); -- '42'
SELECT json_format(JSON 'true'); -- 'true'
SELECT json_format(JSON 'null'); -- 'null'

CAST(json AS VARCHAR) casts the JSON value to the corresponding SQL VARCHAR value. For JSON string, JSON number, true, false or null, the cast behavior is same as the corresponding SQL type. JSON object and JSON array cannot be cast to VARCHAR:

SELECT CAST(JSON '{"a": 1, "b": 2}' AS VARCHAR); -- ERROR!
SELECT CAST(JSON '[1, 2, 3]' AS VARCHAR); -- ERROR!
SELECT CAST(JSON '"abc"' AS VARCHAR); -- 'abc'; Note the double quote is gone
SELECT CAST(JSON '42' AS VARCHAR); -- '42'
SELECT CAST(JSON 'true' AS VARCHAR); -- 'true'
SELECT CAST(JSON 'null' AS VARCHAR); -- NULL

json_parse(string) -> json()¶

Returns the JSON value deserialized from the input JSON text. This is inverse function to json_format():

SELECT json_parse('[1, 2, 3]'); -- JSON '[1,2,3]'
SELECT json_parse('"abc"'); -- JSON '"abc"'

Note

json_parse() and CAST(string AS JSON) have completely different semantics.

json_parse() expects a JSON text conforming to RFC 7159, and returns the JSON value deserialized from the JSON text. The JSON value can be a JSON object, a JSON array, a JSON string, a JSON number, true, false or null:

SELECT json_parse('not_json'); -- ERROR!
SELECT json_parse('{"a": 1, "b": 2}'); -- JSON '{"a": 1, "b": 2}'
SELECT json_parse('[1, 2, 3]'); -- JSON '[1,2,3]'
SELECT json_parse('"abc"'); -- JSON '"abc"'
SELECT json_parse('42'); -- JSON '42'
SELECT json_parse('true'); -- JSON 'true'
SELECT json_parse('null'); -- JSON 'null'

CAST(string AS JSON) takes any VARCHAR value as input, and returns a JSON string with its value set to input string:

SELECT CAST('not_json' AS JSON); -- JSON '"not_json"'
SELECT CAST('{"a": 1, "b": 2}' AS JSON); -- JSON '"{\"a\": 1, \"b\": 2}"'
SELECT CAST('[1, 2, 3]' AS JSON); -- JSON '"[1, 2, 3]"'
SELECT CAST('"abc"' AS JSON); -- JSON '"\"abc\""'
SELECT CAST('42' AS JSON); -- JSON '"42"'
SELECT CAST('true' AS JSON); -- JSON '"true"'
SELECT CAST('null' AS JSON); -- JSON '"null"'

json_size(json, json_path) -> bigint()¶

Like json_extract(), but returns the size of the value. For objects or arrays, the size is the number of members, and the size of a scalar value is zero:

SELECT json_size('{"x": {"a": 1, "b": 2}}', '$.x'); -- 2
SELECT json_size('{"x": [1, 2, 3]}', '$.x'); -- 3
SELECT json_size('{"x": {"a": 1, "b": 2}}', '$.x.a'); -- 0