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                # DBMS 中的外鍵 > 原文: [https://beginnersbook.com/2015/04/foreign-key-in-dbms/](https://beginnersbook.com/2015/04/foreign-key-in-dbms/) **定義**:外鍵是表的列,指向另一個表的[主鍵](https://beginnersbook.com/2015/04/primary-key-in-dbms/)。它們充當表之間的交叉引用。 **例如**: 在下面的例子中,`Course_enrollment`表中的`Stu_Id`列是外鍵,因為它指向`Student`表的主鍵。 `Course_enrollment`表: | `COURSE_ID` | `Stu_Id` | | --- | --- | | C01 | 101 | | C02 | 102 | | C03 | 101 | | C05 | 102 | | C06 | 103 | | C07 | 102 | `Student`表: | `Stu_Id` | `Stu_Name` | `Stu_Age` | | --- | --- | --- | | 101 | Chaitanya | 22 | | 102 | Arya | 26 | | 103 | Bran | 25 | | 104 | Jon | 21 | **注意**:實際上,外鍵與另一個表的主鍵標簽無關,如果它指向另一個表的唯一列(不一定是主鍵),那么它將是一個外鍵。因此,外鍵的正確定義是:外鍵是表的列,指向另一個表的[候選鍵](https://beginnersbook.com/2015/04/candidate-key-in-dbms/)。
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