How to update the tables either in its entirety or not at all

We want update more than two tables at one time,for example we code following:

update A set ***

update B set ***

we first update A, but sometimes B can not be updated sucessful,

How to update A&B tables in its entirety? Or, if any one of these tables can not be updated sucessful,two talbes don't update at all.

Thank you very much?