SQL Server - Index Including PK Lets assume we have a table as follows:

PK -- nonclustered primary key
Col1 -- unique clustered
Col2
Col3


Is this index:

nonclustered index on (Col2, Col3)


any different from this index:

nonclustered index on (Col2, Col3) include (PK)


What if my PK is clustered instead of nonclustered? Now does it make/not make a difference?

Edit to add:

I suppose this is a round-about way of asking: Is the nonclustered index's pointer back to the table based on the clustered index or the primary key? I assume the clustered index RID is what is used.
The clustered index key is included in every non-clustered index as the row identifier.

SQL Server just ignores an INCLUDE of the clustered index key.

If your PK index is NONCLUSTERED then it will not be included in every row of all other NC indexes.

You can test this yourself by making two identical indexes, one with INCLUDE(ClusterKey) and one without, and compare the sizes.  They will be identical, even on hundreds of millions of rows.