可以使用递归cte：

with cte as (
      select '' as chr, '12345' as rest, 0 as lev
      union all
      select left(rest, 1), stuff(rest, 1, 1, ''), lev + 1
      from cte
      where rest <> ''
     )
select chr
from cte
where lev > 0;

要插入到现有表中，只需添加 insert 在 select :

with cte as (
      select '' as chr, '12345' as rest, 0 as lev
      union all
      select left(rest, 1), stuff(rest, 1, 1, ''), lev + 1
      from cte
      where rest <> ''
     )
insert into t (c)
    select chr
    from cte
    where lev > 0;

这是一把小提琴。