12.17.5 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 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:

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 utf8 character type scalars: CHAR, VARCHAR, TEXT, ENUM, and SET
Binary types:
- BLOB: MySQL binary type scalars: BINARY, VARBINARY, BLOB
- BIT: MySQL BIT scalars
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 |
+---------------------+-----------------------+