database - Auto increment an ID with a string prefix in oracle sql? -

i have created following table , wish have userid auto-increment whenever there row added database. id formatted 000001 example below, since there few tables , ideal give each id string prefix:

userid ---------- user000001 user000002 user000003   create table usertable ( userid varchar(20), username varchar(250) not null, firstname varchar(250) not null, lastname varchar(250) not null, constraint pkuserid     primary key (userid), constraint uniusername     unique (username) ); 

you have use combination of trigger , sequence shown in code below:

create sequence create sequence usertable_seq start 1 increment 1 nocache nocycle; /  create or replace trigger usertable_trigger   before insert on usertable each row  begin   select 'user' || to_char(usertable_seq.nextval, '000099')     :new.userid     dual; end; /