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 multiply_10;
multiply_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 n
t_girl(# union all
t_girl(# select m*n, (n-1) n from g where n > 1
t_girl(# )
t_girl-# select max(m) as factorial_10 from g;
factorial_10
--------------
3628800
(1 row)
time: 3.893 ms
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、 用游標和序列函式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 ms
t_girl=#
5、 用自定義python函式
create or replace function func_get_factorial_py(
f_number int
) returns bigint
as $ytt$
m = 1
n = 1
for i in range(1,f_number+1):
m = m * i
n = m
return n
$ytt$
language plpythonu;
t_girl=# select func_get_factorial_py(10) factorial_10;
factorial_10
--------------
3628800
(1 row)
time: 1.060 ms
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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 multiply 10 multiply 10 3628800 1 row ...
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