#difference between primary key and unique key #unique key #unique_key_in_sql

What is the difference between Primary Key and Unique Key ?

1.  We can have only one Primary Key in a table  of Database whereas we can have more than one Unique Key in a table .
2. The Primary Key can not have a NULL value in table whereas a Unique Key may have only
   one null value in column of table.
3. By default, a Primary Key is a Clustered Index whereas by default, a Unique Key is a
   unique non-clustered index in table.
4. A Primary Key supports an Auto Increment value whereas a Unique Key doesn't
   support an Auto Increment value in table.

FAQ question regarding Unique key vs Primary Key 

1. difference between primary key and unique key
2. importance of unique key in sql
3. what is the difference between primary key and unique key
4. importance of unique key in dbms
5. difference between primary key and unique key and foreign key
6. difference between  unique and primary key
7. describe can unique key be null