Don't allow multiple table CONSTRAINTs with the same name.

MariaDB [test]> create table tfk (id INT, c1 INT, c2 INT NOT NULL, CONSTRAINT sid FOREIGN KEY (`c1`) REFERENCES tpk (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION, CONSTRAINT sid check (c2>15));

Query OK, 0 rows affected (0.23 sec)

MariaDB [test]> show create table tfk;

+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

| Table | Create Table                                                                                                                                                                                                                                                                                                   |

+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

| tfk   | CREATE TABLE `tfk` (

  `id` int(11) DEFAULT NULL,

  `c1` int(11) DEFAULT NULL,

  `c2` int(11) NOT NULL,

  KEY `sid` (`c1`),

  CONSTRAINT `sid` FOREIGN KEY (`c1`) REFERENCES `tpk` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,

  CONSTRAINT `sid` CHECK (`c2` > 15)

) ENGINE=InnoDB DEFAULT CHARSET=latin1 |

+-------+-------------------------------------------------------------------------------------------