Count the number of department stores each department store chain has.
select count(*) from department_stores group by dept_store_chain_id
Which department store chain has the largest number of department stores?
select * from department_stores group by dept_store_chain_id order by count(*) desc limit 1
What are the ids of the top two department store chains by number of department stores?
select dept_store_chain_id from department_stores group by dept_store_chain_id order by count(*) desc limit 2