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MySQL 5.7 Reference Manual  /  ...  /  Functions That Return JSON Value Attributes

12.16.5 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 or 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:

  • 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 |
    +---------------------+-----------------------+

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