Create a drop down Regions - Provinces - City

I don't understand why you're using query validation. I'm at a total loss as to what you're trying to do now, sorry. Query validation just takes the value of the field and compares it to a database query to see if the value is valid.

I was looking for another way because you're telling me that the drop down is not a good way, at least that's what I understand. I do in the test with the query that you built for me. I'll let you know if it's okay.

The drop will work to display the values fine, but you won't be able to have the Provinces display based off the Region selected. You'll need to use optgroups to separate them so it looks nicer. Please see the below of an example of a Country field.

www.joomlapolis.com/support/tutorials/107-use-cases/18377-configuring-a-country-field-with-cb-query-field-plugin

You'd basically setup all 3 of your fields to function in the same way.