Re: Nested query performance issue

OK, got to my postgres. Here you are:

create or replace function explode_array(in_array anyarray) returns setof anyelement as
$$
    select ($1)[s] from generate_series(1,array_upper($1, 1)) as s;
$$
language sql immutable;

SELECT s.* FROM score s
WHERE s.id IN (
  select
  -- Get the high scoring score ID for each game:
  explode_array(ARRAY(
      -- Get the high score for game g:
      SELECT s2.id FROM score s2 WHERE s2.game_id = g.id ORDER BY
s2.score DESC LIMIT 5
  ))
  FROM game g
);

It takes ~64ms for me

Best regards, Vitaliy Tymchyshyn