Другие интересные штуки тут: https://t.me/notes_of_programmer
select l.metric
, l.nr as bytes
, case when is_size then pg_size_pretty(nr) end as bytes_pretty
, case when is_size then nr / nullif(x.ct, 0) end as bytes_per_row
from (select min(tableoid) as tbl -- = 'public.tbl'::regclass::oid