I just ran their query, and it works

It does not in PG17.

Works on this Postgres 17.7:

postgres=# show server_version; server_version ------------------------------- 17.7 (Debian 17.7-3.pgdg13+1) (1 row)

postgres=# SELECT sum(blks_hit)/nullif(sum(blks_hit+blks_read),0) AS cache_hit_ratio FROM Pg_stat_database; cache_hit_ratio ------------------------ 0.99448341937558994728 (1 row)