See Part 1 here.
Now you have a good idea of what kind of indices you need for your class and how to define them. Next, how do you handle them?
(REMEMBER: Like any modifications to a class, adding indices in a live system has its risks – if users are accessing or updating data while an index is populated, they may encounter empty or incorrect query results, or even corrupt the indices that are being built.
This is the first in a pair of articles on SQL indices.
Picture the last time you went to a library. Typically they have books sorted by subject matter (and then author and title), and each shelf has an end-plate with a code describing the subject of its books. If you wanted to collect books of a certain subject, instead of walking across every aisle and reading the inside cover of every book, you could head straight for the bookshelf labelled with your desired subject matter and choose your books.
A SQL index has the same general function: