如何将主键作为外部键引用到 MySQL 中的各个表?
mysqlmysqli database
以下是语法 −
alter table yourSecondTableName add constraint `yourConstraintName` foreign key(`yourSecondTableNamePrimaryKey`) references yourFirstTableName(yourFirstTablePrimaryKeyColumnName);
为了理解上述语法，让我们首先创建一个表 −
mysql> create table demo65 −> ( −> id int not null primary key, −> name varchar(20) −> ); Query OK, 0 rows affected (0.57 sec)
以下是创建第二个表的查询 −
mysql> create table demo66 −> ( −> user_id int not null primary key, −> address varchar(200) −> ); Query OK, 0 rows affected (1.80 sec)
以下是将主键引用为外键的查询 −
mysql> alter table demo66 −> add constraint `id_fk` −> foreign key(`user_id`) −> references demo65(id); Query OK, 0 rows affected (3.76 sec) Records: 0 Duplicates: 0 Warnings: 0
让我们使用 SHOW CREATE TABLE 命令检查表的整体描述。以下是查询 −
mysql> show create table demo66;
这将产生以下输出 −
+--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table +--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | demo66 | CREATE TABLE `demo66` ( `user_id` int NOT NULL, `address` varchar(200) DEFAULT NULL, PRIMARY KEY (`user_id`), CONSTRAINT `id_fk` FOREIGN KEY (`user_id`) REFERENCES `demo65` (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci | +--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
