How to search for postal code (ranges)?

I’m sorry, your description is very confusing, so I’m not sure I got it all right. But I’ll try to answer your questions as best I can:

But I won't be able to find something close by, like 89999.

Of course not, you’re filtering for “greater than 9000”. If you want more complex logic, you’ll have to implement that yourself. E.g., filtering for “greater than 8999” might do what you want, depending on what that is. or you could place several filters combined by “OR”.

Additionally, if one place has two zip codes:
89990 and 90010
it seems like, I still receive this as a result (since my search would be right in between the two numbers).

Of course it will be a result, it matches your criteria. Again, if you want more complex logic, you’ll have to implement that yourself.
There is no built-in way (as far as I know) of saying “where ALL values are greater than 9000”.

Worse: If I sort the results by zip code, 89990 comes first - which I haven't entered at all.

This, too, has no built-in way of solving, filtering is completely independent of sorting. Depending on the backend, it might be possible to always use the highest value for sorting, though, if that might help? But I doubt that that’s what you’re looking for.

One more thing:
Any ideas on how to integrate the zip code search with the proximity search from the geo field? Is that possible?

You’ll need some way to translate the ZIP code to a latitude/longitude pair and then use Search API Location → for indexing it and filtering on it.

Please re-open if anything remains unclear.

Thank you very much - Search API Location seems to be the right solution. :)

Automatically closed - issue fixed for 2 weeks with no activity.