mysql中一个表中可以建两个外键关联同一个表中的同一个主键吗？

Question

可以
mysql> create table test1(id int not null auto_increment primary key ,b int);
Query OK, 0 rows affected (0.11 sec)mysql> create table test2(a int,b int);
Query OK, 0 rows affected (0.12 sec)mysql> alter table test2 add CONSTRAINT FOREIGN KEY(a) REFERENCES test1(id);
Query OK, 0 rows affected (0.35 sec)
Records: 0  Duplicates: 0  Warnings: 0mysql> alter table test2 add CONSTRAINT FOREIGN KEY(b) REFERENCES test1(id); 
Query OK, 0 rows affected (0.12 sec)
Records: 0  Duplicates: 0  Warnings: 0mysql> show create table test2;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                             |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test2 | CREATE TABLE `test2` (
  `a` int(11) DEFAULT NULL,
  `b` int(11) DEFAULT NULL,
  KEY `a` (`a`),
  KEY `b` (`b`),
  CONSTRAINT `test2_ibfk_2` FOREIGN KEY (`b`) REFERENCES `test1` (`id`),
  CONSTRAINT `test2_ibfk_1` FOREIGN KEY (`a`) REFERENCES `test1` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)mysql>