Syntax:
JSON_APPEND(json_doc, path, val[, path, val] ...)

Appends values to the end of the indicated arrays within a JSON
document and returns the result. This function was renamed to
JSON_ARRAY_APPEND() in MySQL 5.7.9.

URL: http://dev.mysql.com/doc/refman/5.7/en/json-modification-functions.html

