我卡在了“SQL and Relational Theory”这本书的某一点上,它与关系属性可以采用的类型有关。问题是这样的:
There are exceptions to the rule that relational attributes can be of any type whatsoever, of which one is that if a relation R is of type T, then attributes of R cannot themselves be of type T.
为什么?是不是因为关系 R 的类型是“Relation [name]”,所以属性不能是这种类型?
最佳答案
考虑这样的事情:
create table address {
id int,
name varchar(20),
details address -- the address relation has an attribute that is another of itself
}
定义 将无限递归。
关于sql - C. J. Date 的 "SQL and Relational Theory"中的关系理论,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/13905691/