外键不仅具有标识记录的标识符，而且还具有标识表的一个类型。

The foreign key has not only an identifier to identify a record, but also a type to identify the table.

youdao

外键不仅具有标识记录的标识符，而且还具有标识表的一个类型。

The foreign key has not only an identifier to identify a record, but also a type to identify the table.

youdao