Populate a select options from MySQL

Greetings! I have a MySQL db with 3 tables, for Countries, States and Cities. And I would like it to populate 2 SELECT options in a form. When you select a Country from the first Select Option, populate a second Select Option from with the states table, and then when you select a State, populate the third Select Option with the cities table, and for last, if in the third Select Option, the user selects “Other”, add a text input field where the user can type the name of the city. I attach the SQL file. Thanks!