You can also design more complex boosters, for example, boost by the rating, but...

    You can also design more complex boosters, for example, boost by the rating, 
    but only if the ranking has a certain number of votes. To do this, you can 
    create a function like this:

    create function numericBooster(rating numeric, votes numeric, voteThreshold numeric)
 returns numeric as $$
  select case when votes < voteThreshold then 0 else rating end;
    $$ language sql;

There's really no need to use a function here. It does nothing and makes the code at the call site harder to understand. Additionally, using a function might incur unintended performance penalities. At the very least, the function should be marked IMMUTABLE LEAKPROOF PARALLEL SAFE.