mysql 两个关联表如何更新其中一个表的数据

create table A
(
    order_id int not null auto_increment,
    operator varchar(50),
    oper_date date,
    memo varchar(50),
    primary key(order_id)
);

create table B
(
    order_id int not null auto_increment,
    good_id int,
    good_code int,
    good_name varchar(50),
    memo varchar(50),
    primary key (order_id)
);

insert into A values 
(1,‘onion2‘,now(),‘测试1‘),
(2,‘onion2‘,now(),‘测试2‘),
(3,‘onion3‘,now(),‘测试3‘);

insert into B values
(1,1,0001,‘good1‘,‘已经备注‘);

insert into B (order_id,good_id,good_code,good_name) values 
(2,2,0002,‘good2‘),
(3,3,0003,‘good3‘);

update B,A set B.memo=A.memo
where A.order_id=B.order_id and (B.memo is null or B.memo=‘‘);