I need to do a search for records, such that:

Field_A=x and Field_B=y

Then, I need to run through each of the results, hash them, and do some manipulation of a few other columns, then write it back.

What's the most efficient way to call up the list, hash it, then iterate through it in a loop that I can add the other processes to?

I can see several (at least 2) different ways to do this, and wonder what would be the most efficient?