Let's assume that you have a table that partitions on CATEGORY and SUBCATEGORY. Also assume that every subcategory can be mapped to a category, i.e. subcategory are proper subsets of categories.
Let's also say that for my query, I know I am only interested in a subcategory of 'A', and that I know that everything with a subcategory of A has a category of A.
Which of these should I go with this:
Select blah from blahblah where subcategory = 'A' Select blah from blahblah where subcategory = 'A' and category = 'A';
Which is to say, is the second faster?