員工表 userid

部門表 deptid

員工部門表

條件：一個員工可以對應多個部門

問題：怎么樣設置數據庫，讓其不能重復添加 userid 和deptid？

uuid userid deptid

111

212

311(這個就不能讓其添加)

?

      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');

    

?

備注： 創建聯合索引 create index myindex on employee_dept (employeeid,deptid);