What is the difference between clustered and non-clustered indexes, and how does this relate to simple and compound indexing?

Clustered indexes determine the physical order of data in the table (only one clustered index per table is allowed). Non-clustered indexes are separate structures that point to the data rows. Both simple and compound indexes can be either clustered or non-clustered. A clustered compound index physically sorts the table based on the combined values of the indexed columns. A non-clustered compound index creates a separate index structure with pointers to the data rows, sorted by the combined values of the indexed columns.