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.
1. mysql> SELECT JSON_DEPTH('{}'), JSON_DEPTH('[]'), JSON_DEPTH('true');
2. +------------------+------------------+--------------------+
3. | JSON_DEPTH('{}') | JSON_DEPTH('[]') | JSON_DEPTH('true') |
4. +------------------+------------------+--------------------+
5. | 1 | 1 | 1 |
6. +------------------+------------------+--------------------+
7. mysql> SELECT JSON_DEPTH('[10, 20]'), JSON_DEPTH('[[], {}]');
8. +------------------------+------------------------+
9. | JSON_DEPTH('[10, 20]') | JSON_DEPTH('[[], {}]') |
10. +------------------------+------------------------+
11. | 2 | 2 |
12. +------------------------+------------------------+
13. mysql> SELECT JSON_DEPTH('[10, {"a": 20}]');
14. +-------------------------------+
15. | JSON_DEPTH('[10, {"a": 20}]') |
16. +-------------------------------+
17. | 3 |
18. +-------------------------------+
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.
1. mysql> SELECT JSON_LENGTH('[1, 2, {"a": 3}]');
2. +---------------------------------+
3. | JSON_LENGTH('[1, 2, {"a": 3}]') |
4. +---------------------------------+
5. | 3 |
6. +---------------------------------+
7. mysql> SELECT JSON_LENGTH('{"a": 1, "b": {"c": 30}}');
8. +-----------------------------------------+
9. | JSON_LENGTH('{"a": 1, "b": {"c": 30}}') |
10. +-----------------------------------------+
11. | 2 |
12. +-----------------------------------------+
13. mysql> SELECT JSON_LENGTH('{"a": 1, "b": {"c": 30}}', '$.b');
14. +------------------------------------------------+
15. | JSON_LENGTH('{"a": 1, "b": {"c": 30}}', '$.b') |
16. +------------------------------------------------+
17. | 1 |
18. +------------------------------------------------+
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:
1. mysql> SET @j = '{"a": [10, true]}';
2. mysql> SELECT JSON_TYPE(@j);
3. +---------------+
4. | JSON_TYPE(@j) |
5. +---------------+
6. | OBJECT |
7. +---------------+
8. mysql> SELECT JSON_TYPE(JSON_EXTRACT(@j, '$.a'));
9. +------------------------------------+
10. | JSON_TYPE(JSON_EXTRACT(@j, '$.a')) |
11. +------------------------------------+
12. | ARRAY |
13. +------------------------------------+
14. mysql> SELECT JSON_TYPE(JSON_EXTRACT(@j, '$.a[0]'));
15. +---------------------------------------+
16. | JSON_TYPE(JSON_EXTRACT(@j, '$.a[0]')) |
17. +---------------------------------------+
18. | INTEGER |
19. +---------------------------------------+
20. mysql> SELECT JSON_TYPE(JSON_EXTRACT(@j, '$.a[1]'));
21. +---------------------------------------+
22. | JSON_TYPE(JSON_EXTRACT(@j, '$.a[1]')) |
23. +---------------------------------------+
24. | BOOLEAN |
25. +---------------------------------------+
JSON_TYPE() returns NULL if the argument is NULL:
1. mysql> SELECT JSON_TYPE(NULL);
2. +-----------------+
3. | JSON_TYPE(NULL) |
4. +-----------------+
5. | NULL |
6. +-----------------+
An error occurs if the argument is not a valid JSON value:
1. mysql> SELECT JSON_TYPE(1);
2. ERROR 3146 (22032): Invalid data type for JSON data in argument 1
3. 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 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.
1. mysql> SELECT JSON_VALID('{"a": 1}');
2. +------------------------+
3. | JSON_VALID('{"a": 1}') |
4. +------------------------+
5. | 1 |
6. +------------------------+
7. mysql> SELECT JSON_VALID('hello'), JSON_VALID('"hello"');
8. +---------------------+-----------------------+
9. | JSON_VALID('hello') | JSON_VALID('"hello"') |
10. +---------------------+-----------------------+
11. | 0 | 1 |
12. +---------------------+-----------------------+

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Document created the 26/06/2006, last modified the 26/10/2018
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References

Manuel MySQL : https://dev.mysql.com/

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