Question

在SQL中，如何在复合主键上创立外键？

外键如何和表的复合主键建立关系
create table s
(
sid varchar(20),
sname varchar(20),
ssex varchar(2) check(ssex='男' or ssex='女') default '男',
sage int check(sage between 0 and 100),
sclass varchar(20),
constraint event_key primary key (sid,sclass)----创建复合主键
)
create table t
(
teacher varchar(20) primary key,
tclass varchar(20) foreign key references s(sclass),----复合外键怎么创？
num int
)
外键不可以单一的对应复合主键里的一个键而建立么吗？

Answer 1

--不能一列引用两列，必髯数列对应
use tempdb
go
create table s
(
sid varchar(20),
sname varchar(20),
ssex varchar(2) check(ssex='男' or ssex='女') default '男',
sage int check(sage between 0 and 100),
sclass varchar(20),
constraint event_key primary key (sid,sclass)----创建复合主键
)

create table t
(
teacher varchar(20) primary key,
sid varchar(20) not null,
sclass varchar(20) not null,
num int,
foreign key(sid,sclass) references s(sid,sclass)
)

Answer 2

语法：
①创建时：create table sc (
studentno int,
courseid int,
score int,
foreign key (courseid) );
②修改时：
ALTER TABLE news_info[子表名] ADD CONSTRAINT FK_news_info_news_type[约束名] FOREIGN KEY (info_id)[子表列] REFERENCES news_type[主表名] (id)[主表列] 。