当我以表格形式更新数据时，必须从tables book中减去colbook的数量-1。请用扳机帮忙
表格形式

Create table Form (
idForm int not null primary key auto_increment,
date_of_issue date not null,
return_date date ,
idBook int not null,
Foreign key(idBook) references Book (idBook));

台账

Create table Book (
idBook int not null primary key auto_increment,
name varchar(45) not null,
colBook int(11) null;

填表

Insert into Form (idForm, date_of_issue)
Values(1, "2018-11-11");

填表

Insert into Book (idBook, name, colBook)
Values(1, Garri Potter, 5);

表格更新申请表

update Form
set return_date = "2000-03-03"
where idBook = 1;