Msql 联结索引

员工表 userid

部门表 deptid

员工部门表

条件：一个员工可以对应多个部门

问题：怎么样设置数据库，让其不能重复添加 userid 和deptid？

uuid userid deptid

111

212

311(这个就不能让其添加)

?

DROP TABLE IF EXISTS `dept`;CREATE TABLE `dept` (  `id` int(11) NOT NULL AUTO_INCREMENT,  `deptname` char(32) NOT NULL,  PRIMARY KEY (`id`)) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;-- ------------------------------ Records of dept-- ----------------------------INSERT INTO `dept` VALUES ('1', '1');INSERT INTO `dept` VALUES ('2', '2');

?

DROP TABLE IF EXISTS `employee`;CREATE TABLE `employee` (  `id` int(11) NOT NULL AUTO_INCREMENT,  `name` varchar(32) NOT NULL,  PRIMARY KEY (`id`)) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;-- ------------------------------ Records of employee-- ----------------------------INSERT INTO `employee` VALUES ('1', '11');

?

DROP TABLE IF EXISTS `employee_dept`;CREATE TABLE `employee_dept` (  `id` int(11) NOT NULL,  `employeeid` int(11) NOT NULL,  `deptid` int(11) NOT NULL,  PRIMARY KEY (`id`),  KEY `bb` (`deptid`),  KEY `myindex` (`employeeid`,`deptid`),  CONSTRAINT `aa` FOREIGN KEY (`employeeid`) REFERENCES `employee` (`id`),  CONSTRAINT `bb` FOREIGN KEY (`deptid`) REFERENCES `dept` (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8;-- ------------------------------ Records of employee_dept-- ----------------------------INSERT INTO `employee_dept` VALUES ('1', '1', '1');INSERT INTO `employee_dept` VALUES ('2', '1', '2');

?

备注：创建联合索引create index myindex on employee_dept (employeeid,deptid);