Difference between Unique key and Primary Key..
1. By default primary key will generate clustered index
where as unique key will generate Non-clustered index.
2. Primary key is a combination of unique and NOT NULLConstraint.
So it can't have duplicate value/any NULLs .
Where as unique Key can have any number of Nulls.
3. A table can have only one Primary key.
But it can have number of unique key.