By default, JSON_COMPOSE returns a LOB based JSON document with character set UNICODE and a maximum length of 32000 UNICODE characters (64000 bytes), unless otherwise specified with the optional RETURNS clause.
A hierarchical relationship is not possible with this function. The resulting JSON document is flat, with each input parameter corresponding to one child of the result. The resulting document are in this format:
{
name1 : data1,
name2 : data2,
...,
nameN : dataN,
}
If a value used to compose the JSON document is a Vantage NULL, that value is returned in the JSON instance as a JSON null.