11111111111111111111111111

-- Create sequence
create sequence RELATION_SEQUENCE                      
minvalue 1              
maxvalue 999999999999999999999999999 
start with 1
increment by 1
cache 20;
COMMIT;
-- 建立触发器
create or REPLACE trigger relation_trigger before
insert on tb_relation for each row
begin
select RELATION_SEQUENCE.nextval into:new.relation_id from dual;
end;
COMMIT;