Script for preventing duplicate entries when uploading from spreadsheet

Script for preventing duplicate entries when uploading from spreadsheet

Hi, newbie/free user here --

This seems like a popular question, but I can't find a solution that quite matches what I need. Still confused, hoping for help.

I want to use Zoho to manage my contacts, and keep an equivalent/periodically updated .xls on my desktop. This way, I can update contacts even when I'm not online (while on a flight, for example) and load them in as soon as it's convenient.

I can't figure out a way to do this without reuploading a lot of duplicates every time. The answer is probably that I need to script something, but I'm having trouble understanding how to do that and got error messages each time I tried.

Some of my contacts have all fields filled out, some have almost none (company, first name, last name, title, phone, email, it's fairly standard). Some companies have multiple people, so I can't set "company" to not accept duplicates.

Any help is greatly, greatly appreciated. I don't have budget to move to a paid program yet, so if this isn't feasible with the free option I'll revert back to some less-nifty option.

Thanks again.