Coalesce/EmptyString function not working

Hello!

I have a challenge to overcome and I hope some of you can help me out here.

I have a special need and I need to check 4 different email attributes in the target mapping before sending out emails to some particular customers.

We have 4 attributes in the recipient table and the hierarchy is as follow:

@457687- if populated we send the communication 

@825706- we use it if 1 is empty 

@1304489- we use it if 1 and 2 are empty 

@1424983- we use it if 1,2 and 3 are empty

I tried to use some functions (coalesce and emptyString) but I cannot get a correct result and changing the architecture is unfortunately not an option.

So I need to use a function in the email target mapping that works as explained. 

Thanks in advance