JSON functions

[beikov]

The idea is to add some functions to query and manipulate JSON.
Also see https://modern-sql.com/blog/2017-06/whats-new-in-sql-2016

Construction

• json_object(k1,v1[,kn,vn]*) - constructor function that creates a json object
• json_array(v1[,vn]*) - constructor function that creates a json array
• json_parse(payload) - parses a json object

Query

• json_arrayagg(any) within group (...) - aggregates json objects into a json array
• json_objectagg(key, value) - aggregates key-values into a single json object
• json_value(json, jsonpath [returning <type>] ) - returns a scalar value for the path where can be number, boolean or string (default)
• json_exists(json, jsonpath) true if the JSON document contains a value for the path expression, and false otherwise
• json_query(json, jsonpath) returns a json document

Manipulation

• json_concat(json, json)
• json_set(json, jsonpath, element) - returns a JSON having the given path set with the given element

Track HHH-18496 for progress.