Hi,
Answering my own question:
I was eventually able to make my query fit as "construction" instead of "free" by putting the two tables and their alias in the table field. I also managed to make it work by removing the "mandatory" values for parent and value in the database if I used the "free" query type.
I had other queries for which I had issues with the size of the table fields in the Select Dynamic Cascade (too many characters for the series of tables) that I solved by creating an SQL view with a shorter name.
I had a problem to save the values though with the second option but I solved it by declaring the method as "POST" instead of "GET". (I have another topic for this specific issue).
Regards.
Xav.