Alternative key or secondary key is combination of unique key +not null

No both are not same . It is true that Unique+Not null and Primary Key allow same restrictions on data but there is a diff that column with primary key contain a Clustered index but column with Unique Key+Null Contain a Non-Clustered index.

No both are not same . It is true that Unique+Not null and Primary Key allow same restrictions on data but there is a diff that column with primary key contain a Clustered index but column with Unique Key+Null Contain a Non-Clustered index.....

yes they are totally equal