What is difference between unique key with 'not null' constraint and primary key?
sql, sql-server-2008
Solution
A primary key must be unique and non-null, so they're the same from that standpoint. However, a table can only have one primary key, while you can have multiple unique non-null keys.
Most systems also use metadata to tag primary keys separately so that they can be identified by designers, etc.
What are the differences between a primary key and a Unique key with not null constrain in terms of how they are stored in database
If both are either `CLUSTERED` or `NON CLUSTERED` then the only difference is metadata in most systems to tag a index as a PK.
what difference are there when we making `Select`,`Insert`,`Update`, `Delete` operation for these keys
None.
Problem
I want to know difference between these two key. When the Unique key with `not null` constrain in terms of how they are stored in database and what difference are there when we making `Select,Insert,Update, Delete` operation for these keys.