Now, you just can’t talk about indexing in SQL Server really without talking about filtered indexes. They are a very, very important thing. Conceptually, they are just not that hard to figure out.
It’s an index with a where clause. It only indexes some of the data. It qualifies for the where clause. I don’t know. Like the benefits of that just seem rather apparent to me.
Benjamin Franklin highly encourages you to watch this video, even though filtered indexes are one of the most frustrating things in SQL Server. There are so many cases where I think they should work, and they actually work in approximately a third of those cases.