14.17.5 Functions That Return JSON Value Attributes

The functions in this section return attributes of JSON values.

• JSON_DEPTH(json_doc)

  Returns the maximum depth of a JSON document. Returns NULL if the argument is NULL. An error occurs if the argument is not a valid JSON document.

  An empty array, empty object, or scalar value has depth 1. A nonempty array containing only elements of depth 1 or nonempty object containing only member values of depth 1 has depth 2. Otherwise, a JSON document has depth greater than 2.

  mysql> SELECT JSON_DEPTH('{}'), JSON_DEPTH('[]'), JSON_DEPTH('true');
  +------------------+------------------+--------------------+
  | JSON_DEPTH('{}') | JSON_DEPTH('[]') | JSON_DEPTH('true') |
  +------------------+------------------+--------------------+
  |                1 |                1 |                  1 |
  +------------------+------------------+--------------------+
  mysql> SELECT JSON_DEPTH('[10, 20]'), JSON_DEPTH('[[], {}]');
  +------------------------+------------------------+
  | JSON_DEPTH('[10, 20]') | JSON_DEPTH('[[], {}]') |
  +------------------------+------------------------+
  |                      2 |                      2 |
  +------------------------+------------------------+
  mysql> SELECT JSON_DEPTH('[10, {"a": 20}]');
  +-------------------------------+
  | JSON_DEPTH('[10, {"a": 20}]') |
  +-------------------------------+
  |                             3 |
  +-------------------------------+

• JSON_LENGTH(json_doc[, path])

  Returns the length of a JSON document, or, if a path argument is given, the length of the value within the document identified by the path. Returns NULL if any argument is NULL or the path argument does not identify a value in the document. An error occurs if the json_doc argument is not a valid JSON document or the path argument is not a valid path expression. Prior to MySQL 8.0.26, an error is also raised if the path expression contains a * or ** wildcard.

  The length of a document is determined as follows:

  • The length of a scalar is 1.

  • The length of an array is the number of array elements.

  • The length of an object is the number of object members.

  • The length does not count the length of nested arrays or objects.

  mysql> SELECT JSON_LENGTH('[1, 2, {"a": 3}]');
  +---------------------------------+
  | JSON_LENGTH('[1, 2, {"a": 3}]') |
  +---------------------------------+
  |                               3 |
  +---------------------------------+
  mysql> SELECT JSON_LENGTH('{"a": 1, "b": {"c": 30}}');
  +-----------------------------------------+
  | JSON_LENGTH('{"a": 1, "b": {"c": 30}}') |
  +-----------------------------------------+
  |                                       2 |
  +-----------------------------------------+
  mysql> SELECT JSON_LENGTH('{"a": 1, "b": {"c": 30}}', '$.b');
  +------------------------------------------------+
  | JSON_LENGTH('{"a": 1, "b": {"c": 30}}', '$.b') |
  +------------------------------------------------+
  |                                              1 |
  +------------------------------------------------+

• JSON_TYPE(json_val)

  Returns a utf8mb4 string indicating the type of a JSON value. This can be an object, an array, or a scalar type, as shown here:

  mysql> SET @j = '{"a": [10, true]}';
  mysql> SELECT JSON_TYPE(@j);
  +---------------+
  | JSON_TYPE(@j) |
  +---------------+
  | OBJECT        |
  +---------------+
  mysql> SELECT JSON_TYPE(JSON_EXTRACT(@j, '$.a'));
  +------------------------------------+
  | JSON_TYPE(JSON_EXTRACT(@j, '$.a')) |
  +------------------------------------+
  | ARRAY                              |
  +------------------------------------+
  mysql> SELECT JSON_TYPE(JSON_EXTRACT(@j, '$.a[0]'));
  +---------------------------------------+
  | JSON_TYPE(JSON_EXTRACT(@j, '$.a[0]')) |
  +---------------------------------------+
  | INTEGER                               |
  +---------------------------------------+
  mysql> SELECT JSON_TYPE(JSON_EXTRACT(@j, '$.a[1]'));
  +---------------------------------------+
  | JSON_TYPE(JSON_EXTRACT(@j, '$.a[1]')) |
  +---------------------------------------+
  | BOOLEAN                               |
  +---------------------------------------+

  JSON_TYPE() returns NULL if the argument is NULL:

  mysql> SELECT JSON_TYPE(NULL);
  +-----------------+
  | JSON_TYPE(NULL) |
  +-----------------+
  | NULL            |
  +-----------------+

  An error occurs if the argument is not a valid JSON value:

  mysql> SELECT JSON_TYPE(1);
  ERROR 3146 (22032): Invalid data type for JSON data in argument 1
  to function json_type; a JSON string or JSON type is required.

  For a non-NULL, non-error result, the following list describes the possible JSON_TYPE() return values:

  • Purely JSON types:

    • OBJECT: JSON objects

    • ARRAY: JSON arrays

    • BOOLEAN: The JSON true and false literals

    • NULL: The JSON null literal

  • Numeric types:

    • INTEGER: MySQL TINYINT, SMALLINT, MEDIUMINT and INT and BIGINT scalars

    • DOUBLE: MySQL DOUBLE FLOAT scalars

    • DECIMAL: MySQL DECIMAL and NUMERIC scalars

  • Temporal types:

    • DATETIME: MySQL DATETIME and TIMESTAMP scalars

    • DATE: MySQL DATE scalars

    • TIME: MySQL TIME scalars

  • String types:

    • STRING: MySQL utf8mb3 character type scalars: CHAR, VARCHAR, TEXT, ENUM, and SET

  • Binary types:

    • BLOB: MySQL binary type scalars including BINARY, VARBINARY, BLOB, and BIT

  • All other types:

    • OPAQUE (raw bits)

• JSON_VALID(val)

  Returns 0 or 1 to indicate whether a value is valid JSON. Returns NULL if the argument is NULL.

  mysql> SELECT JSON_VALID('{"a": 1}');
  +------------------------+
  | JSON_VALID('{"a": 1}') |
  +------------------------+
  |                      1 |
  +------------------------+
  mysql> SELECT JSON_VALID('hello'), JSON_VALID('"hello"');
  +---------------------+-----------------------+
  | JSON_VALID('hello') | JSON_VALID('"hello"') |
  +---------------------+-----------------------+
  |                   0 |                     1 |
  +---------------------+-----------------------+