"Original" PostgreSQL implementation Factorial method enumeration

PostgreSQL function is huge, to achieve multiplication this kind of operation has many methods, today I will briefly enumerate the following several convenient ways.

Like we're counting 10!

1, you can use SQL to expand it:

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. With recursion

t_girl=# with recursive g (M,n) as t_girl-# (select 1 m, Ten 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. Use simple functions to expand

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 (Ten) as factorial_10; Factorial_10--------------3628800 (1 row) time:1.022 ms

4. Use cursors and Sequence function generate_series to expand

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. Use custom Python functions

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 (Ten) factorial_10; Factorial_10--------------3628800 (1 row) time:1.060 ms

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"Original" PostgreSQL implementation Factorial method enumeration