trying to create a trigger on supabase to calculate a winrate based on two other columns

create
or replace function calculate_winrate () returns trigger as $$
begin
    new.winrate = (new.wins / (new.wins + new.losses)) * 100;
    return new;
end;
$$ language plpgsql;

create
or replace trigger calculate_winrate_trigger
before
update on "mtg-player_deck" for each row
execute function calculate_winrate ();