How to obtain the free space size in a JSON table column using the JSON_STORAGE_FREE() function?

JSON_STORAGE_FREE(json) is a MySQL built-in function that returns the free space size in a JSON table column.

Free space occurs when JSON table column is partially updated with less data. For example:

CREATE TABLE jtable (jcol JSON);
INSERT INTO jtable VALUES ('{"a": 1000, "b": "FYIcenter", "c": "[1, 3]"}');

SELECT jcol, JSON_STORAGE_FREE(jcol) AS Size FROM jtable; 
  -- +----------------------------------------------+------+
  -- | jcol                                         | Size |
  -- +----------------------------------------------+------+
  -- | {"a": 1000, "b": "FYIcenter", "c": "[1, 3]"} |    0 |
  -- +----------------------------------------------+------+

UPDATE jtable SET jcol = JSON_SET(jcol, "$.b", "FYI");

SELECT jcol, JSON_STORAGE_FREE(jcol) AS Size FROM jtable;
  -- +----------------------------------------+------+
  -- | jcol                                   | Size |
  -- +----------------------------------------+------+
  -- | {"a": 1000, "b": "FYI", "c": "[1, 3]"} |    6 |
  -- +----------------------------------------+------+

If you call JSON_STORAGE_FREE() will a JSON value, not a table column, it will returns 0. For example:

SELECT JSON_STORAGE_FREE('[100, "FYI", [1, 3, 5], 425.05]');
  -- +------------------------------------------------------+
  -- | JSON_STORAGE_FREE('[100, "FYI", [1, 3, 5], 425.05]') |
  -- +------------------------------------------------------+
  -- |                                                    0 |
  -- +------------------------------------------------------+

Reference information of the JSON_STORAGE_FREE() function:

JSON_STORAGE_FREE(json): int
  Returns the free space in a given JSON table column resulted 
  from previous partial updates. 

Arguments, return value and availability:
  json: Required. The JSON table column to be examined.
  int: Return value. The the free space in the JSON column.
  Available since MySQL 8.0.

Related MySQL functions:

• JSON_STORAGE_SIZE() - Storage Size of JSON Value
• JSON_STORAGE_FREE() - Free Space in JSON Value

⇒ JSON_INSERT() - Inserting Members to JSON Value

⇐ JSON_EXTRACT() - Exacting Members from JSON

⇑ MySQL Functions on JSON Values

⇑⇑ MySQL Function References