oracle 求阶乘

//求阶乘
//数学里面最直接的阶乘定义就是，将这个数n乘以n-1,再乘以n-1-1,一直乘到1,
//所得到的结果就是n的阶乘:n!=n*(n-1)*(n-1)*...*2*1,这里要注意：0!=1
//下面定义一个球阶乘的函数：
create or replace function fun_factorial(num number)
return number 
is 
  result number:=1;
begin   
   if num<0 then
      raise_application_error(-20012,' function parameters can not be less than zero');
   elsif num=0 or num=1 then 
      return 1;
   else
      for i in 2..num loop
          result:=i*result;
      end loop;
      return result;
   end if;
end fun_factorial;
/
SQL> select fun_factorial(5) from dual;
FUN_FACTORIAL(5)
----------------
             120
//
SQL> select fun_factorial(6) from dual; 
FUN_FACTORIAL(6)
----------------
             720
//当我们给阶乘函数传递负数时，我们将得到最初设定的错误
select fun_factorial(-6) from dual
ORA-20012:  function parameters can not be less than zero
ORA-06512: at "YEEXUN.FUN_FACTORIAL", line 7
//
//如果有这样的要求呢？
//n!+(n-1)!+(n-2)!+...+2!+1!
//我们该怎么处理呢？
create or replace function fun_sum_of_factorial(n number)
return number
as
  results number:=0;
begin 
     //下面使用nvl(n,5)为了保证用户有输入，如果没有输入数据，默认为5
     for i in 1..nvl(n,5)
     loop
         //这里调用了上面我们创建的fun_factorial函数，求每一个数的阶乘
         //然后再将每个数的阶乘相加就能得到结果了
         results := results + fun_factorial(i);
     end loop;
     return results;
     exception
       when others then
         dbms_output.put_line(sqlerrm);
end fun_sum_of_factorial;
/
SQL> select fun_sum_of_factorial(5) from dual;
FUN_SUM_OF_FACTORIAL(5)
-----------------------
                    153
//
SQL> select fun_sum_of_factorial(50) from dual;
FUN_SUM_OF_FACTORIAL(50)
------------------------
     3.10350532295462E64
//
//如果能用一句话写出来那该多好啊!
//
select sum(nm)
from (
     select power(2,sum(log(2,level)) over(order by level)) nm
     from dual
     connect by level<=5)
/
   SUM(NM)
----------
       153

更多求阶乘方法：

http://space.itpub.net/12932950/viewspace-664600

原帖：

http://topic.csdn.net/u/20110516/16/b3761513-8ddd-4668-bc5d-cfb970e827c4.html?51453