//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