Choose a query by a select value

Hi guys,
I’ve a question.
I’ve a page with a foto gallery inside it.
I want to apply different queries according to the value of a select.
I mean, there is a select with 2 option:

• shows all pictures

• shows only the picturs with relations with city (it’s just an example)

So there must be two different server actions each one with its own query or one server action
with a conditionl tree:
(if the select value is then query 1, else query 2).
I want the page runs the right query according to the value of the select.

This is the link to the page:
https://www.campaniaturismo.org/test_room/test_select_and_queries.php

Has someone an idea?
Thank you guys