I am new to Databases and while i was studying about constraints in SQL. I came across Primary Key, Unique Key, Not Null Constraints. As per my understanding a primary key is used to uniquely identify a column in a table and cannot have null values. A unique key can have one Null Values and cannot contain duplicate values. A not null constraint doesn't allow us to enter null value in the column.
My question is: Why should i apply Primary key on a column if i can get the same functionality by applying Unique and Not Null Constraints together on a column.
Can anyone explain this to me. Thanks in advance.