Question

CREATE TABLE abc 
(
    id INT NOT NULL,
    class VARCHAR(10) NOT NULL,
    division VARCHAR(1) NOT NULL,
    dateOfxyz DATE NOT NULL,
    PRIMARY KEY (id, class, division, dateOfxyz)
)

现在，我想在另一个表中访问此主键的id类和分区部分作为外键，我可以这样做吗？如果是，那怎么样？

Answer 1

我不明白你的问题 在引用表中，必须有一个索引，其中外键列以相同的顺序列为第一列。 https://dev.mysql.com/doc/refman/5.6/en/create-table-foreign-keys.html

MariaDB [sandbox]> drop table if exists t;
Query OK, 0 rows affected (0.03 sec)

MariaDB [sandbox]>
MariaDB [sandbox]> CREATE TABLE abc
    -> (
    -> id INT NOT NULL,
    -> class VARCHAR(10) NOT NULL,
    -> division VARCHAR(1) NOT NULL,
    -> dateOfxyz DATE NOT NULL,
    -> PRIMARY KEY (id, class, division, dateOfxyz)
    -> );
ERROR 1050 (42S01): Table 'abc' already exists
MariaDB [sandbox]>
MariaDB [sandbox]> drop table if exists t;
Query OK, 0 rows affected, 1 warning (0.00 sec)

MariaDB [sandbox]> create table t
    -> (id INT NOT NULL,
    -> class VARCHAR(10) NOT NULL,
    -> division VARCHAR(1) NOT NULL);
Query OK, 0 rows affected (0.03 sec)

MariaDB [sandbox]>
MariaDB [sandbox]> alter table t
    -> add foreign key tfk1(id,class,division) references abc(id,class,division);
Query OK, 0 rows affected (0.12 sec)
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [sandbox]>
MariaDB [sandbox]> show create table t;
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                          |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t     | CREATE TABLE `t` (
  `id` int(11) NOT NULL,
  `class` varchar(10) NOT NULL,
  `division` varchar(1) NOT NULL,
  KEY `tfk1` (`id`,`class`,`division`),
  CONSTRAINT `tfk1` FOREIGN KEY (`id`, `class`, `division`) REFERENCES `abc` (`id`, `class`, `division`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |

我可以在另一个表中使用复合键的一个属性作为外键吗？

1 个答案: