Whats is mean by primary key and unique key?
Primary Key:- Primary Key is an attribute or a set of attributes in a table which uniquely identifies a record (row) in a table and no two records (rows) in the table can have the same values for all the columns comprising the primary key.
Unique Key:- A unique key is a key which stores unique values (no duplicates) for that particular column.
Difference between Primary Key & Unique Key:-
A Unique key can store a null value and primary key cannot store any null value.
A primary key can be references to another table as a Foreign Key.