Question

I need to create a hash key on my tables for uniqueness and someone mentioned to me about md5. But I have read about checksum and binary sum; would this not serve the same purpose? To ensure no duplicates in a specific field.
Now I managed to implement this and I see the hask keys in my tables.
Do I need to alter index keys originally created since I created a new index key with these hash keys? Also do I need to change the keys?
How do I change my queries for example SELECT statements?
I guess I am still unsure how hash keys really help in queries other than uniqueness?

Answer 1

There’s always the HashBytes() function. It supports md5, but if you don’t like it there’s an option for sha1.

As for how this can help queries: one simple example is if you have a large varchar column — maybe varchar max — and in your query you want to know if the contents of this column match a particular string. If you have to compare your search with every single record it could be slow. But if you hash your search string and use that, things can go much faster since now it’s just a very short binary compare.