PostgreSQL 實現階乘方法列舉

標籤：postgresql   function   階乘   

PostgreSQL 功能龐大，對實現乘法這類運算有諸多的方法，今天我來簡單列舉下以下幾種便捷的途徑。

比如我們要計算10！

1、 可以用SQL給它展開：

t_girl=# select 1*2*3*4*5*6*7*8*9*10 as mutiply_10;     mutiply_10 ------------    3628800(1 row)Time: 0.854 ms

2、 用WITH遞迴

t_girl=# with recursive g(m,n) as t_girl-# (select 1 m, 10 nt_girl(# union allt_girl(# select m*n, (n-1) n from g where n > 1t_girl(# )t_girl-# select max(m) as factorial_10 from g; factorial_10 --------------      3628800(1 row)Time: 3.893 ms

3、 用簡單的函數來展開

create or replace function func_get_factorial(f_number int)  returns bigint as $ytt$  declare i int :=1;  declare v_result bigint := 1;begin  for i in 1 .. f_number loop    v_result := v_result * i;  end loop;  return v_result;end;$ytt$ language plpgsql;t_girl=# select func_get_factorial(10) as factorial_10; factorial_10 --------------      3628800(1 row)Time: 1.022 ms

4、 用遊標和序列函數generate_series來展開

create or replace function func_get_factorial2(f_number int)  returns bigint as $ytt$  declare cs1 cursor for select n from generate_series(1,f_number,1) as g(n);  declare v_result bigint := 1;  declare v_n bigint := 0;begin    open cs1;    loop        fetch cs1 into v_n;        exit when not found;v_result := v_result * v_n;    end loop;    close cs1;  return v_result;end;$ytt$ language plpgsql;t_girl=# select func_get_factorial2(10) factorial_10; factorial_10 --------------      3628800(1 row)Time: 2.238 mst_girl=# 

5、 用自訂python函數

create or replace function func_get_factorial_py(f_number int)  returns bigint as $ytt$m = 1n = 1for i in range(1,f_number+1):    m = m * in = mreturn n$ytt$ language plpythonu;t_girl=# select func_get_factorial_py(10) factorial_10; factorial_10 --------------      3628800(1 row)Time: 1.060 ms

PostgreSQL 實現階乘方法列舉