Your key = 'article_body' is an array JSON, so you need to use index get the data.

You can try this.

Schema (MySQL v5.7)

CREATE TABLE wc_article_full_data(

   full_article_json JSON
);

insert into wc_article_full_data values (
'{"article_body" : [
    {
        "article_desc" : "THURSDAY, Sept. 1, 2016 (HealthDay News) -- Dapagliflozin improves insulin sensitivity and increases lipid oxidation and plasma ketone concentration in patients with type 2 diabetes mellitus (T2DM), according to a study published online Aug. 25 in Diabetes Care.  Giuseppe Daniele",
        "links" : [{
                "link_name" : "Full Text (subscription or payment may be required)"}
        ]}
]}');

Query #1

SELECT JSON_EXTRACT(full_article_json,'$.article_body[0].article_desc') AS descriptio
FROM wc_article_full_data;

| descriptio                                                                                                                                                                                                                                                                                 |
| ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| "THURSDAY, Sept. 1, 2016 (HealthDay News) -- Dapagliflozin improves insulin sensitivity and increases lipid oxidation and plasma ketone concentration in patients with type 2 diabetes mellitus (T2DM), according to a study published online Aug. 25 in Diabetes Care.  Giuseppe Daniele" |

View on DB Fiddle

If you want to get all value from article_desc which from article_body array. you can try to use* in index.

SELECT JSON_EXTRACT(full_article_json,'$.article_body[*].article_desc') AS descriptio
FROM wc_article_full_data

Possible realization:

WITH RECURSIVE cte AS ( SELECT @from num
                        UNION ALL
                        SELECT num+1 FROM cte WHERE num < @till )
SELECT CONCAT('key', num) `key`, 
       JSON_EXTRACT(test.val, CONCAT('$.key', num)) `value`
FROM test
CROSS JOIN cte
HAVING `value` IS NOT NULL;

fiddle

test_tbl:

+----+------------------+
| id | json_col         |
+----+------------------+
|  2 | {"a": 2, "b": 5} |
|  3 | {"c": 3, "a": 5} |
|  4 | {"d": 1, "c": 7} |
|  5 | {"e": 1, "f": 7} |
+----+------------------+

Using JSON_TABLE in Mysql 8.0:

SELECT DISTINCT json_key FROM test_tbl,
    json_table(
        json_keys(json_col),
        '$[*]' COLUMNS(json_key JSON PATH '$')
    ) t;

Results:

+----------+
| json_key |
+----------+
| a        |
| b        |
| c        |
| d        |
| e        |
| f        |
+----------+

There is a way to solve this in SQL 5.7. I will go step by step in composing the solution. The goal is to find the strength of the knight.

I am going to use the same sample table as previous post:

create table mytable ( mycol json );

insert into mytable set mycol = '[{"Race": "Orc", "strength": 14}, {"Race": "Knight", "strength": 7}]';

First, get an array of only the races.

select json_extract(mycol, '$[*].Race') from mytable;
+----------------------------------+
| json_extract(mycol, '$[*].Race') |
+----------------------------------+
| ["Orc", "Knight"]                |
+----------------------------------+

Then, search for the Knight in this array (and unquote it).

select json_unquote(json_search(json_extract(mycol, '$[*].Race'), 'one', 'Knight')) from mytable;
+------------------------------------------------------------------------------+
| json_unquote(json_search(json_extract(mycol, '$[*].Race'), 'one', 'Knight')) |
+------------------------------------------------------------------------------+
| $[1]                                                                         |
+------------------------------------------------------------------------------+

Having found the index, get this element from the array.

select json_extract(mycol, json_unquote(json_search(json_extract(mycol, '$[*].Race'), 'one', 'Knight'))) from mytable;
+---------------------------------------------------------------------------------------------------+
| json_extract(mycol, json_unquote(json_search(json_extract(mycol, '$[*].Race'), 'one', 'Knight'))) |
+---------------------------------------------------------------------------------------------------+
| {"Race": "Knight", "strength": 7}                                                                 |
+---------------------------------------------------------------------------------------------------+

Then get the strength of this element.

select json_extract(json_extract(mycol, json_unquote(json_search(json_extract(mycol, '$[*].Race'), 'one', 'Knight'))), '$.strength') as strength from mytable;
+----------+
| strength |
+----------+
| 7        |
+----------+

You can repeat this on other fields to create other columns.