JSON_ARRAY_IGNORE_NULL

Description

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

Syntax

JSON_ARRAY_IGNORE_NULL([<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_IGNORE_NULL 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 ignored. If you DO want to retain null values in the array, you can use the function JSON_ARRAY.
• 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_IGNORE_NULL(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_IGNORE_NULL(JSON_PARSE('{"key": "value"}'));

Examples

1. Regular parameters

   select json_array_ignore_null() as empty_array, json_array_ignore_null(1) v1, json_array_ignore_null(1, 'abc') v2;

   +-------------+------+-----------+
   | empty_array | v1   | v2        |
   +-------------+------+-----------+
   | []          | [1]  | [1,"abc"] |
   +-------------+------+-----------+

2. NULL parameters

   select json_array_ignore_null(null) v1, json_array_ignore_null(1, null, 'I am a string') v2;

   +------+---------------------+
   | v1   | v2                  |
   +------+---------------------+
   | []   | [1,"I am a string"] |
   +------+---------------------+

3. Unsupported parameter types

   select json_array_ignore_null('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_ignore_null(1, cast(map('key', 'value') as json));

   +--------------------------------------------------------------+
   | json_array_ignore_null(1, cast(map('key', 'value') as json)) |
   +--------------------------------------------------------------+
   | [1,{"key":"value"}]                                          |
   +--------------------------------------------------------------+

5. JSON strings can be parsed with json_parse

   select json_array_ignore_null(json_parse('{"key1": "value", "key2": [1, "I am a string", 3]}'));

   +------------------------------------------------------------------------------------------+
   | json_array_ignore_null(json_parse('{"key1": "value", "key2": [1, "I am a string", 3]}')) |
   +------------------------------------------------------------------------------------------+
   | [{"key1":"value","key2":[1,"I am a string",3]}]                                          |
   +------------------------------------------------------------------------------------------+