You seem to be looking for cases with more than 1 address alias, which can be detected by having a comma (",") in the alias column.

So maybe this will work:

SELECT nr

, case when alias not like '%,%' then NULL else [address] end

, case when alias not like '%,%' then NULL else alias end

from @info

That's not very efficient, but your info table isn't even in 1st normal form and efficiency is not going to happen when you start off with a table which is disastrously deficient in normalisation.