title: Check whether sqlalchemy table is empty
body: <p>I need to know whether any given sqlalchemy table (sqlalchemy.schema.Table) has exactly 0 rows.  I have a lot of tables with a lot of rows in each and this has to run for all of them at startup so I am looking for the most efficient way to do this from a runtime perspective. So, just doing a count is not what I am looking for. The database is PostgreSQL if that changes anything</p>