Lets say I have two tables

customer table has cuid, name, gender, cityid
city table has cityid, cityname, citysize

And they are joined together like this

select cuid, name, cityname, citysize
from customer cu
left outer join city ct on cu.cityid = ct.id

1. How can I edit that only customer table is updated?
2. If I want to edit both at the same time, how do I do that instead?

Thanks