Cb query issue

Ok !
This Works perfect !
Better to work at dawn, fresh mind...

Oups...Sorry, it almost work...
I have all the states field, not just the one selected... 

Again, copy and paste the solution from our demo site. You have a fully functioning example that you can freely explore there. I have no idea what else to advice you on in this regard. We also have the below tutorial, which is old but still valid.

www.joomlapolis.com/documentation/345-cb-query-field/tutorials/18533-configuring-dynamic-usa-state-city-zip-fields-with-cb-query-field-plugin

I did all that, during hours...
May I suggest a demo website up to date ?
I mean using the comprofiler_countries and comprofiler_provinces tables as they are provided natively, I suppose they are also on this demo website, but they're not used for the demo, so I suppose an exemple related to the actual version would be usefull for me, and I suppose for some others, even you, as you wouldn't have to answer to this message.
Problem is I have absolutely no view on the database of the demo site, so it's a bit hard to guess what I'm missing here.

Also, into CB Core Field Ajax / General / Display Empty Update On, while set to disable, I suppose I should not see the field if there's no data right ? So, here I always see the field if there's no state.
Should I understand things differently ?

I've got a single query dropdown, how should I get all the states of the entries ?
 

Those tables are not native to CB. They're provided by CBSubs, which is why we provide an example not dependent on CBSubs. An example of how to query those tables using CB Query Field is in the Query Autocomplete under Integrations > CB Query Field of the following fields.

cb_address_country
cb_address_state

You can adapt these to used for query select if you so choose. Below are some topics doing exactly that.

www.joomlapolis.com/forum/developer-members-support/240757-query-drop-down-single-select-displaying-value-not-label-after-update?start=6#311513

www.joomlapolis.com/forum/cb-paid-subscriptions-support/241845-cbsubs-invoice-fields-problem#315497

www.joomlapolis.com/forum/developer-members-support/236894-solved-mapping-of-address-fields-to-cbsubs-not-working?start=0#295537

Well, thanks for pointing additionnal ressources, at some point I'll find my way...
In the meantime, I doubt arguing that CB sub does not natively belong to CB, and say that is the reason why you're not providing example to fully connect them together, on the website of the creator of CB and CB sub, is a good call.