MySQL完整性约束条件

create table person
 ( id char(10),
 age smallint,
 name char(10),
 spouse char(10),
 primary key(id),
 foreign key(spouse) references person(id) on delete set null on update cascade,
 check(age>0));
//key(attr1) references table(attr2)要注意,delete,update针对attr2