Hi Flavia, the best option is to have a reliable person identifier. In your case, you probably have the SSN somewhere in your source data, as I am sure that info is necessary on a loan. I used to work at a bank and investment firms, so I know that access to that field may be restricted, but do you have some kind of masked identifier or person identifier to work with? I think I would find these folks in your database before bringing the data to tableau. And personally, I would never bring SSNs into Tableau (unless maybe my company had bought Tableau server, and even then I would use some masked identifier or key if at all possible).
So in your database, you can retrieve customers who have never been approved by doing something like the following...
select cust_id, home_phone, cell_phone, email, etc.
where cust_id =
group by cust_id
having max(case when status = 'Approved' then 1 else 0 end) = 0) sub;
If you don't have access to the SSN or some customer identifier, I'd ask someone with clearance to it to run this query and return to you the records with some key instead of an SSN that you can use as a customer identifier to tie together phone, email, etc. to one person.
Hope this gets you started. Even if you get the results of this query, you might get multiple records per cust_id. Say someone uses one email address on 1st application, and another on a second application. In this case, you can decide you will send follow-ups to both email addresses, or you could make your query find and return only the single most recent address. These decisions will need to be made according to your company's rules and preferences.
It is great to see how other people will approach this-- it is true that I can't use SSN, and there is no customer ID.
Each situation is slightly complicated because of limitation of here and there, but the process writing (thinking how to write) and reading the thread helps me to think clearer. Thank you Jennifer for the ideas!!