mysql数据库操作之通过修改表的时候添加外键
语法代码：
- alter table 从表 add foreign key(公共字段) references 主表(公共字段)
- drop table if exists stuinfo;
- create table stuinfo(
- id tinyint primary key,
- name varchar(20)
- )engine=innodb;
- drop table if exists stuscore;
- create table stuscore(
- sid tinyint primary key,
- score tinyint unsigned
- )engine=innodb;
- alter table stuscore add foreign key (sid) references stuinfo(id)
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