Indexes, Part 3: Clustered vs Non-Clustered

The Difference

Imagine you have a bookstore. You need to sort it somehow. You can sort by author, by genre, by length, or by name. But you have to choose. This will be your key, and the books can only be ordered one way. You can't simultaneously order by author and by name — you just have a certain amount of books, and they can only sit on the shelf in one order.

Let's say you decide to order by name, alphabetically, and you don't care about author or genre. This is your CLUSTERED KEY and CLUSTERED INDEX.