How do you create an auto increment in Oracle 11g?

You have to modify the sequence as follows :

CREATE SEQUENCE sequence_staffMINVALUE 1000000START WITH 1000000INCREMENT BY 1 NOCACHE NOCYCLE;

Also, you have to insert the new staff_id column using sequence_staff.nextval always. See how it works hitting

select sequence_staff.nextval from dual; --repeated times.

Read more about sequences here https://docs.oracle.com/cd/B28359_01/server.111/b28310/views002.htm

EDIT :

Yes, it is possible. Create sequence the way you were creating and :

select to_char(sequence_staff.nextval,'FM0000000') from dual;

EDIT 2 :

This link deserves the credit. http://stackoverflow.com/questions/14561210/creating-a-sequence-for-a-varchar2-field-in-oracle

EDIT 3 : If you really want the results your way in Oracle Database you have to :

1. alter table staff modify staff_id varchar(20);2. CREATE SEQUENCE sequence_staffMINVALUE 1START WITH 1INCREMENT BY 1 NOCACHE NOCYCLE;3. insert into staff(Staff_id, surname,firstnames, phone,address) values(to_char(sequence_staff.nextval,'FM0000000'),'Wayne','Bruce','0000','Gotha‌​m'); 

CREATE TABLE staff     (         id         NUMBER(7) NOT NULL,             surname    VARCHAR2(50) NOT NULL,                 firstnames VARCHAR2(50) NOT NULL,                     phone      VARCHAR2(30) NOT NULL,                         address    VARCHAR2(150) NOT NULL   );ALTER TABLE Staff ADD (  CONSTRAINT staff_pk PRIMARY KEY (ID));    CREATE SEQUENCE staff_seq START WITH 1;

Trigger definition:

            CREATE OR REPLACE TRIGGER staff_bir                 BEFORE INSERT ON Staff                     FOR EACH ROW                        BEGIN                            SELECT staff_seq.NEXTVAL                                INTO   :new.id                                    FROM   dual;                                       END;