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An identity column is a column associated with an internal sequence generator and has it value automatically set when omitted in an INSERT statement.

Example:

create table objects (
id integer generated by default as identity primary key,
name varchar(15)
);

insert into objects (name) values (‘Table’);
insert into objects (name) values (‘Book’);
insert into objects (id, name) values (10, ‘Computer’);

select * from objects;

ID NAME
============ ===============
1 Table
2 Book
10 Computer