生成自然顺序，和自定义顺序的编号
select 'E' || trim(to_char(nvl(a, 0), '00000000')) customer_id--固定位数填充
from (select t.a, t1.a b
from (select rownum a
from dual
connect by rownum <=
(select max(to_number(replace(customer_id, 'E', ''))) + 2
from tb_cus_firm
where customer_id like 'E%')) t,
(select to_number(replace(customer_id, 'E', '')) a
from tb_cus_firm
where customer_id like 'E%') t1
where t.a not like '%4%' and t.a = t1.a(+))
where b is null and rownum = 1
解析：
select a,rownum
from (select t.a, t1.a b
from (select rownum a
from dual
connect by rownum <=
(select max(to_number(replace(customer_id, 'E', ''))) + 2
from tb_cus_firm
where customer_id like 'E%')) t,
(select to_number(replace(customer_id, 'E', '')) a
from tb_cus_firm
where customer_id like 'E%') t1
where t.a not like '%4%' and t.a = t1.a(+))
/*where b is null*/ /*and rownum = 1*/ rownum是根据当前的结果集在作用域内变化，这句就保证了跳过之后还从未用的顺序开始
同样的两列比较：取理论上对比实际为null的那些的第一个