postgis - How could you calculate the distance between multiple associated points, specifically a list of structures serving specific addresses within CartoDB?

I have loaded two point datasets into CartoDB. The first is a list of structures serving specific addresses, each structure has a unique code associated to it as well as the location of the structure itself. The other point dataset is a list of the addresses and their locations, each address having the code of the structure that serves it.

I know how to calculate the distance of each structure from each address, however this seems quite inefficient when all I require is the distance between the structure serving the address in question (the other structures I'm not worried about for any given address).

Note I only require the great circle (haversine) distance. Also, if the same query can determine which of the addresses lie X distance (in km) away from the structure serving it that would be great.

Any ideas on how you'd go about this within CartoDB/PostgreSQL?