Is a primary key automatically an index?

Question

If I run Profiler, then it suggests a lot of indexes like this one

CREATE CLUSTERED INDEX [_dta_index_Users_c_9_292912115__K1] ON [dbo].[Users]  (  [UserId] ASC )WITH (SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF,  ONLINE = OFF) ON [PRIMARY] 

UserId is the primary key of the table Users. Is this index better than the one already in the table:

ALTER TABLE [dbo].[Users] ADD  CONSTRAINT [PK_Users] PRIMARY KEY NONCLUSTERED  (  [UserId] ASC )WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, SORT_IN_TEMPDB = OFF,  IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS  = ON,  ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY] 

Answer 1

Yes a primary key is always an index.

If you don't have any other clustered index on the table, then it's easy: a clustered index makes a table faster, for every operation. YES! It does. See Kim Tripp's excellent The Clustered Index Debate continues for background info.

So really, every useful table (except for maybe staging tables for bulkload or another few rare cases) ought to have a clustered index. If you don't have one, it's quite obvious the DTA would recommend one, and put it on the Primary Key column(s) by default.