With in the JSON it is very touch to split the values from Parameters while we connect to REST connector.
A, B, C, D
FROM JSON (wrap on) "root"
WITH CONNECTION (
QUERY "ProductId" "$(vProductId)");
Load A, B, C, D, SubField("root", '@') as "root" Resident RC;
Here "root" is my Query parameters which constantly stored in REST connector section.