SELECT concat(
json_extract(additional,'$.surname'),
json_extract(additional,'$.firsname'),
json_extract(additional,'$.lastname')
)
FROM `user_attributes`
"Петров""Петр""Петрович"
SELECT concat(
JSON_UNQUOTE(json_extract(additional,'$.surname')),
JSON_UNQUOTE(json_extract(additional,'$.firsname')),
JSON_UNQUOTE(json_extract(additional,'$.lastname'))
) fullname
FROM `user_attributes`
;