Question

How does the PRIMARY KEY keyword relate to clustered indexes in SQL Server?

(Some people seem to want to answer this question instead of a different question I asked, so I am giving them a better place to do so.)

Answer 1

The clustered index of a table is normally defined on the primary key columns.

This, however is not a strict requirement.

From MSDN:

When you create a PRIMARY KEY constraint, a unique clustered index on the column or columns is automatically created if a clustered index on the table does not already exist and you do not specify a unique nonclustered index.

And:

You can create a clustered index on a column other than primary key column if a nonclustered primary key constraint was specified.