Design idea and recommendation

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PHP

Ajax

Hi all,

I'm wondering which would be the right way to enter a place in the database...

Let me explain it:

I have a table named tPlaces which includes fields like:

Country, State/province, City, Postal code, GPS coordinates, name of this place, ...
When I want to enter a new place, probably some of the data will exist already:

Multiple customers from the same country...

When I have to enter the new country, I could add a combobox in the form, but that would be helpful only if the country is already introduced into the database.
Same would happen with the city...

I could put an editbox with some ajax to reduce the list possibilities while I write (OnKeyUp...) but this would end giving me a country name in a variable.

Or I could add a combobox and an editbox... and, if I change the combobox it should overwrite the value of the editbox...

What is done in situations like this to make it easy for the user?

Thank you all...

What I have tried:

Searching for form examples...