What is primary key?

Answer 1

Primary key is nothing but Unique means no duplication should be
Example I'd like 1,2,3 are unique no same I'd should be their

Answer 2

Its a columns that contains a unique value for each row, so you can identify the row on querys. For example: if you are making a "persons" table, the passport number would be a good primary key, cause each row (person) will have an unique value, and therefore, its easy to identify this person whenever you need so

Answer 3

something Unique

Answer 4

unique identification given to each records of the database table