How many membership registrations are there in 2016?
select count(*) from membership_register_branch where register_year = 2016
What about for each branch?
select branch_id, count(*) from membership_register_branch where register_year = 2016 group by branch_id
Show me the name of branch with the most of them.
select t2.name from membership_register_branch as t1 join branch as t2 on t1.branch_id = t2.branch_id where t1.register_year = 2016 group by t2.branch_id order by count(*) desc limit 1
What about its open year?
select t2.name, t2.open_year from membership_register_branch as t1 join branch as t2 on t1.branch_id = t2.branch_id where t1.register_year = 2016 group by t2.branch_id order by count(*) desc limit 1