Oracle primary key auto increment setting

 -- Create table
 CREATE TABLE tb_demo
 (
     id INT NOT NULL,
     key1 VARCHAR2(40) NULL,
     key2 VARCHAR2(40) NULL
 );

-- Set primary key
alter table tb_demo add constraint tb_demo_pk primary key (id);

-- New sequence
 create sequence tb_demo_id
 minvalue 1
 nomaxvalue 
 increment by 1 
 start with 1
 nocache;
 
 
 -- New trigger
 create or replace trigger tb_demo_tg_insertId
 before insert on tb_demo for each row 
 begin
   select tb_demo_id.Nextval into:new.id from dual;
 end;
 
 -- insert data
 insert into tb_demo (key1, key2)
 values ('key1', 'key2');
 insert into tb_demo (key1, key2)
 values ('key11', 'key22');
 
 -- Query table
 select * from tb_demo;

 -- Query the current sequence value
 select tb_demo_id.currval from dual;