Today we continue our series with our second question of the day.

What is the difference between a clustered and non-clustered index?

In simplest terms, a clustered index is the actual data, reordering the way that the records are physically stored.  Because of this, each table can only contain one clustered index.

However, a non-clustered index is more like a pointer to the actual record.  The logical order of the non-clustered index does not usually match how the data is stored physically.

There is also a third option, the heap, which is a table without an index at all.  Without an index, the server would have to read through all of the records in order to find the data queried.  Enjoy!