How many purchases are there in 2018?
select count(*) from purchase where year = 2018
How many of them were made through any branch in London?
select count(*) from purchase as t1 join branch as t2 on t1.branch_id = t2.branch_id where t2.city = 'London' and t1.year = 2018
Show me the sum of total pounds of them.
select sum(total_pounds) from purchase as t1 join branch as t2 on t1.branch_id = t2.branch_id where t2.city = 'London' and t1.year = 2018