关联表UPDATE问题

Question

a
id,total_amountb
id,a_id,amounta,b一对多,统计出a.total_amount是多少,这句UPDATE SQL如何写

Answer 1

怎么会是UPDATE呢
select a.total_amount where a.id = b.id;

Answer 2

select sum(b.amount) from a,b where a.id = b.a_id;update b set total_amount='' where b.id=''

Answer 3

select a.id,sum(b.amount) from a,b where a.id = b.a_id;