show the id of the shops that have a happy hour.
select shop_id from happy_hour
just show those that have happy hours in May.
select shop_id from happy_hour where month = 'May'
return their addresses too.
select t1.address, t1.shop_id from shop as t1 join happy_hour as t2 on t1.shop_id = t2.shop_id where month = 'May'