Primary Key:
1. Primary Key is used to identify all the records in a relation uniquely.
2. Primary key can not have null value.
3. Primary key can be only one per table.
4. Primary key creats clustered index.
Unique key:
1. Unique key is also used to identify a records uniquely.
2. Unique key can accept one null value.
3. Unique key can be multiple in a table.
4. Unique key creates non-clustered index.