比如有2个表
readertype:
typeid(primary key)
typename
booknumber.....
reader:
readerid(primary key)
readername
readertype.....
由于typename不是主键,所以就不能readertype设为外键,将而我要想在typename和readertype建立类似外键的约束关系,请问如何解决
readertype:
typeid(primary key)
typename
booknumber.....
reader:
readerid(primary key)
readername
readertype.....
由于typename不是主键,所以就不能readertype设为外键,将而我要想在typename和readertype建立类似外键的约束关系,请问如何解决
create table a1(produce varchar(10) primary key)
insert into a1 select 'A'
insert into a1 select 'B'
insert into a1 select 'C'
insert into a1 select 'D'
insert into a1 select 'E'create table a2(produce varchar(10) not null
foreign key references a1(produce) on delete cascade
on update cascade--建表时就这样定义(更新与删除)
,val int)
insert into a2 select 'A',1
insert into a2 select 'B',2
insert into a2 select 'C',3
insert into a2 select 'D',4
insert into a2 select 'E',5测试更新:
update a1
set produce='A1'
where produce='A'
select * from a2alter table a2 add constraint a2_con foreign key(produce)references a1(produce) on delete cascade on update cascade
delete from a1 where produce='a'
select * from a1
select * from a2drop table a1,a2
readertype,在查询的时候直接join readertype表来获得呢?