First, some blah... blah... blah... By default when a primary key constrained is created on a table/view, SQL Server automatically creates a unique clustered in order to enforce it. And since a table can only have one clustered index, all the subsequent or any previous indexes created before that are created as a non-clustered index. That works best in most cases and is the recommended best practice. And decision to have clustered index on what columns affects everything about everyday working of an application. And also as a general best practice every table should have a clustered index, but its not required and there are cases where its best not to. Scenario: So now imagine a scenario where a table has the PK but the clustered index is on non PK columns. I am going to assume that there must be well thought-out index strategy for that particular table at the design time. But over time the usage patterns may evolve and/or through endless enhancements, bug fixes etc. now tha...