SQL Server performance optimization

I have table to store files. I store SHA256 hash in a column to uniquely identify a file. Before inserting new file I check for duplicate file using the hash and if it exists already I don’t insert.

For example my query can be:

select filename 
from filetable 
where filehash = 'xyz'

Right now there are only a few hundred files.

When this number grows to a few hundred thousand next year, how do I optimize the performance?

Answer

For that specific query just add the index:

create index ix1 on filetable (filehash);

If you want to make it even faster (probably not needed) you can create a covering index instead:

create index ix1 on filetable (filehash, filename);