How to remove null attributes from my JSON in MySQL - mysql

Question

I am having a table which is storing the JSON values. Within these JSONs, the JSON is having null attributes like below :
{
"name" : "AAAA",
"department" : "BBBB",
"countryCode" : null,
"languageCode" : null,
"region" : "AP"
}
I would like to write a query so that all the null attributes are removed from the output. For e.g. for the above-mentioned JSON, the resultant output JSON should be like this.
{
"name" : "AAAA",
"department" : "BBBB",
"region" : "AP"
}
I would like to have a generic query which I can apply to any JSON to get rid of null attributes in MySQL (v5.7).

Answer 1

In case you don't know all the keys in advance:
WITH j AS (SELECT CAST('{"a": 1, "b": "null", "c": null}' AS JSON) o)
SELECT j.o, (SELECT JSON_OBJECTAGG(k, JSON_EXTRACT(j.o, CONCAT('$."', jt.k, '"')))
FROM JSON_TABLE(JSON_KEYS(o), '$[*]' COLUMNS (k VARCHAR(200) PATH '$')) jt
WHERE JSON_EXTRACT(j.o, CONCAT('$."', jt.k, '"')) != CAST('null' AS JSON)) removed
FROM j;
Outputs:
o
removed
{"a": 1, "b": "null", "c": null}
{"a": 1, "b": "null"}
And this will keep your keys with string value "null", which is different from json null.

Answer 2

The following query will work for removing a single key value pair, where the value is NULL:
SELECT JSON_REMOVE(col, '$.countryCode')
FROM yourTable
WHERE CAST(col->"$.countryCode" AS CHAR(50)) = 'null';
But, I don't see a clean way of doing multiple removals in a single update. We could try to chain the updates together, but that would be ugly and non readable.
Also, to check for your JSON null, I had to cast the value to text first.
Demo

Answer 3

How you can remove null keys using JSON_REMOVE function. $.dummy is used if the condition is false.
select json_remove(abc,
case when json_unquote(abc->'$.name') = 'null' then '$.name' else '$.dummy' end,
case when json_unquote(abc->'$.department') = 'null' then '$.department' else '$.dummy' end,
case when json_unquote(abc->'$.countryCode') = 'null' then '$.countryCode' else '$.dummy' end,
case when json_unquote(abc->'$.languageCode') = 'null' then '$.languageCode' else '$.dummy' end,
case when json_unquote(abc->'$.region') = 'null' then '$.region' else '$.dummy' end)
from (
select cast('{
"name" : "AAAA",
"department" : "BBBB",
"countryCode" : null,
"languageCode" : null,
"region" : "AP"
}' as json) as abc ) a
Output:
{"name": "AAAA", "region": "AP", "department": "BBBB"}