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JSON_ARRAY

Description​

Generate a JSON array containing the specified elements. Returns an empty array when no parameters are passed.

Syntax​

JSON_ARRAY([<expression>, ...]) 

Parameters​

Variable parameters:​

  • <expression>: Elements to be included in the JSON array. Can be single or multiple values of different types, including NULL.

Return Value​

JSON: Returns a JSON array composed of the parameter list.

Usage Notes​

  • JSON_ARRAY implementation converts different types of parameters to JSON values by implicitly calling the TO_JSON function, so parameters must be types supported by TO_JSON
  • NULL will be converted to JSON null. If you don't want to retain null values in the array, you can use the function JSON_ARRAY_IGNORE_NULL.
  • If the parameter type is not supported by TO_JSON, you will get an error. You can first convert that parameter to String type, for example:
    select JSON_ARRAY(CAST(NOW() as String));

    The NOW() function returns a DateTime type, which needs to be converted to String type using the CAST function

  • If the parameter is a JSON string and you want to add it to the array as a JSON object, you should explicitly call the JSON_PARSE function to parse it as a JSON object:
    select JSON_ARRAY(JSON_PARSE('{"key": "value"}'));

Examples​

  1. Regular parameters
    select json_array() as empty_array, json_array(1) v1, json_array(1, 'abc') v2;
    +-------------+------+-----------+
    | empty_array | v1 | v2 |
    +-------------+------+-----------+
    | [] | [1] | [1,"abc"] |
    +-------------+------+-----------+
  2. NULL parameters
    select json_array(null) v1, json_array(1, null, 'I am a string') v2;
    +--------+--------------------------+
    | v1 | v2 |
    +--------+--------------------------+
    | [null] | [1,null,"I am a string"] |
    +--------+--------------------------+
  3. Unsupported parameter types
    select json_array('item1', map(123, 'abc'));
    ERROR 1105 (HY000): errCode = 2, detailMessage = Can not find the compatibility function signature: to_json(MAP<TINYINT,VARCHAR(3)>)
  4. Map type parameters can be explicitly converted to JSON
    select json_array(1, cast(map('key', 'value') as json));
    +--------------------------------------------------+
    | json_array(1, cast(map('key', 'value') as json)) |
    +--------------------------------------------------+
    | [1,{"key":"value"}] |
    +--------------------------------------------------+
  5. The JSON string will be added to the array in the form of a string
    select json_array('{"key1": "value", "key2": [1, "I am a string", 3]}');
    +------------------------------------------------------------------+
    | json_array('{"key1": "value", "key2": [1, "I am a string", 3]}') |
    +------------------------------------------------------------------+
    | ["{\"key1\": \"value\", \"key2\": [1, \"I am a string\", 3]}"] |
    +------------------------------------------------------------------+
  6. A JSON string can be parsed using json_parse and then passed to json_array
    select json_array(json_parse('{"key1": "value", "key2": [1, "I am a string", 3]}'));
    +------------------------------------------------------------------------------+
    | json_array(json_parse('{"key1": "value", "key2": [1, "I am a string", 3]}')) |
    +------------------------------------------------------------------------------+
    | [{"key1":"value","key2":[1,"I am a string",3]}] |
    +------------------------------------------------------------------------------+