add docs

docs/en/sql-reference/functions/json-functions.md

@@ -471,3 +471,38 @@ Result:
 
 -   [output_format_json_quote_64bit_integers](../../operations/settings/settings.md#session_settings-output_format_json_quote_64bit_integers)
 -   [output_format_json_quote_denormals](../../operations/settings/settings.md#settings-output_format_json_quote_denormals)
+
+
+## JSONArrayLength
+
+Returns the number of elements in the outermost JSON array. The function returns NULL if input JSON string is invalid.
+
+**Syntax**
+
+``` sql
+JSONArrayLength(json)
+```
+
+Alias: `JSON_ARRAY_LENGTH(json)`.
+
+**Arguments**
+
+-   `json` — [String](../../sql-reference/data-types/string.md) with valid JSON.
+
+**Returned value**
+
+-   If `json` is a valid JSON array string, returns the number of array elements, otherwise returns NULL.
+
+Type: [Nullable(UInt64)](../../sql-reference/data-types/int-uint.md).
+
+**Example**
+
+``` sql
+SELECT
+    JSONArrayLength(''),
+    JSONArrayLength('[1,2,3]')
+
+┌─JSONArrayLength('')─┬─JSONArrayLength('[1,2,3]')─┐
+│                ᴺᵁᴸᴸ │                          3 │
+└─────────────────────┴────────────────────────────┘
+```

tests/queries/0_stateless/02667_json_array_length.sql

@@ -1,13 +1,16 @@
 -- { echoOn }
-select json_array_length(null);
-select json_array_length('');
-select json_array_length('[]');
-select json_array_length('[1,2,3]');
-select json_array_length('[[1,2],[5,6,7]]');
-select json_array_length('[{"a":123},{"b":"hello"}]');
-select json_array_length('[1,2,3,[33,44],{"key":[2,3,4]}]');
-select json_array_length('{"key":"not a json array"}');
-select json_array_length('[1,2,3,4,5');
+select JSONArrayLength(null);
+select JSONArrayLength('');
+select JSONArrayLength('[]');
+select JSONArrayLength('[1,2,3]');
+select JSONArrayLength('[[1,2],[5,6,7]]');
+select JSONArrayLength('[{"a":123},{"b":"hello"}]');
+select JSONArrayLength('[1,2,3,[33,44],{"key":[2,3,4]}]');
+select JSONArrayLength('{"key":"not a json array"}');
+select JSONArrayLength('[1,2,3,4,5');
 
-select json_array_length(2); -- { serverError ILLEGAL_TYPE_OF_ARGUMENT }
-select json_array_length(); -- { serverError NUMBER_OF_ARGUMENTS_DOESNT_MATCH }
+select JSON_ARRAY_LENGTH('[1,2,3,4,5');
+select JSON_ARRAY_LENGTH('[1,2,3,4,5]');
+
+select JSONArrayLength(2); -- { serverError ILLEGAL_TYPE_OF_ARGUMENT }
+select JSONArrayLength(); -- { serverError NUMBER_OF_ARGUMENTS_DOESNT_MATCH }