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 mutiply_10;     Mutiply_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 (Ten) factorial_10; Factorial_10--------------      

5. Use custom Python functions

Create or Replace function func_get_factorial_py (f_number int)  returns bigint as $ytt $m = 1n = 1for i in range (1,f_num ber+1):    m = m * in = Mreturn n$ytt$ language plpythonu;t_girl=# Select Func_get_factorial_py (Ten) factorial_10; Factori Al_10--------------      3628800 (1 row) time:1.060 ms

PostgreSQL implementation Factorial Method enumeration