One of each occurence from table

I have a table of IP addresses and DNS names (of failed hackers, as it happens).

I want to search by DNS name (or part), eg, yetanotherhacker1234.ttnet.net.tr, or just *ttnet.net.tr and find all IP addresses matching that DNS.

However, that could bring back hundreds if not thousands of results, particularly in the case of scripted attacks where there may be 500 or more failed attacks from the same IP address.

So, I want only to see one instance of each IP address for each DNS, eg:

ttnet.net.tr -> 11.22.33.44
ttnet.net.tr -> 11.22.44.66
ttnet.net.tr -> 11.22.55.88

Obviously this could be done by finding all records for the DNS, ordered by IP address, then looping through them and only displaying a record if the IP differed from the previous record. However that seems very inefficient, particularly when there may be thousands of records.

So I need a better way - any solutions gratefully received.

Ta.