In MariaDB, JSON_DEPTH() is a built-in function that allows you to check the depth of a JSON document.

It accepts the JSON document as an argument, and returns the maximum depth of the document.

Syntax

The syntax goes like this:

JSON_DEPTH(json_doc)

Where json_doc is the JSON document for which to return the depth.

Example

Here’s an example to demonstrate.

SELECT JSON_DEPTH('{ "name": "Wag" }');

Result:

+---------------------------------+
| JSON_DEPTH('{ "name": "Wag" }') |
+---------------------------------+
|                               2 |
+---------------------------------+

In this case, the depth is 2.

Scalar Values & Empty Objects/Arrays

Scalar values or empty arrays or objects have a depth of 1:

SELECT 
    JSON_DEPTH('{}'),
    JSON_DEPTH('[]'),
    JSON_DEPTH(1);

Result:

+------------------+------------------+---------------+
| JSON_DEPTH('{}') | JSON_DEPTH('[]') | JSON_DEPTH(1) |
+------------------+------------------+---------------+
|                1 |                1 |             1 |
+------------------+------------------+---------------+

Deeper JSON Document

Here’s an example that uses a JSON document with a depth of 4:

SET @json_document = '
    { 
        "_id" : 1, 
        "name" : "Wag", 
        "details" : {
            "type" : "Dog", 
            "weight" : 20,
            "awards" : { 
                "Florida Dog Awards" : "Top Dog", 
                "New York Marathon" : "Fastest Dog", 
                "Sumo 2020" : "Biggest Dog"
            }
        }
    }
';
SELECT JSON_DEPTH(@json_document);

Result:

+----------------------------+
| JSON_DEPTH(@json_document) |
+----------------------------+
|                          4 |
+----------------------------+

Null Arguments

If the argument is NULL, the result is NULL:

SELECT JSON_DEPTH(null);

Result:

+------------------+
| JSON_DEPTH(null) |
+------------------+
|             NULL |
+------------------+

Invalid JSON

Passing invalid JSON results in NULL with a warning:

SELECT JSON_DEPTH('{1}');

Result:

+-------------------+
| JSON_DEPTH('{1}') |
+-------------------+
|              NULL |
+-------------------+
1 row in set, 1 warning (0.000 sec)

Let’s see the warning:

SHOW WARNINGS;

Result:

+---------+------+--------------------------------------------------------------------------------+
| Level   | Code | Message                                                                        |
+---------+------+--------------------------------------------------------------------------------+
| Warning | 4038 | Syntax error in JSON text in argument 1 to function 'json_depth' at position 2 |
+---------+------+--------------------------------------------------------------------------------+

Incorrect Parameter Count

Providing no arguments results in an error:

SELECT JSON_DEPTH();

Result:

ERROR 1582 (42000): Incorrect parameter count in the call to native function 'JSON_DEPTH'

It’s the same when you provide too many arguments:

SELECT JSON_DEPTH('{"a": 1}', 2);

Result:

ERROR 1582 (42000): Incorrect parameter count in the call to native function 'JSON_DEPTH'