create extension weighted_stats;
create temp table test as (
  select a::numeric, b::numeric 
  from 
    generate_series(1, 100) as a(a),
    generate_series(1, 100) as b(b));
select weighted_mean(a,b) from test;
    weighted_mean    
---------------------
 50.5000000000000000
(1 row)

update test set b = 0;
select weighted_mean(a,b) from test;
 weighted_mean 
---------------
             0
(1 row)