Of course there is a table “pg_stat_all_tables” and column “n_live_tup” – but this number is only an estimation based on statistics.
If you would like to know exactly and you want to see it in order and you do not mind to nearly kill your server you can try one of these selects:
In one particular schema and database:
with srcdata as ( select schemaname||'.'||tablename as _table from pg_tables where schemaname in ('...here_your_schema...') order by _table )
select s._table, t._count from srcdata s
join lateral
(select * from dblink('dbname=...your_database...', 'select '''||s._table||'''::text as _table, count(*)::bigint as _count from '||s._table)
as t(_table text, _count bigint) ) t on s._table=t._table
order by _count desc
Variant for parent and child tables:
with srcdata as ( select inhrelid::regclass::text as child, inhparent::regclass::text as parent from pg_inherits order by parent, child )
select s.parent, s.child, t._count from srcdata s
join lateral (select * from dblink('dbname=...your_database...', 'select '''||s.child||'''::text as child, count(*)::bigint as _count from '||s.child)
as t(child text, _count bigint) ) t on s.child=t.child
order by _count desc