MySQL

Question

因为我可以从多个 table 中获取记录而忽略重复项，例如我有这个 table "code attached tables":

SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for interests
-- ----------------------------
DROP TABLE IF EXISTS `interests`;
CREATE TABLE `interests` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of interests
-- ----------------------------
INSERT INTO `interests` VALUES ('1', 'Sport');
INSERT INTO `interests` VALUES ('2', 'Technology');
INSERT INTO `interests` VALUES ('3', 'Games');
INSERT INTO `interests` VALUES ('4', 'Security');
INSERT INTO `interests` VALUES ('5', 'Movies');

-- ----------------------------
-- Table structure for interests_has_user
-- ----------------------------
DROP TABLE IF EXISTS `interests_has_user`;
CREATE TABLE `interests_has_user` (
  `interests_id` int(10) unsigned NOT NULL,
  `user_id` int(10) unsigned NOT NULL,
  PRIMARY KEY (`interests_id`,`user_id`),
  KEY `fk_interests_has_user_user1_idx` (`user_id`),
  KEY `fk_interests_has_user_interests_idx` (`interests_id`),
  CONSTRAINT `fk_interests_has_user_interests` FOREIGN KEY (`interests_id`) REFERENCES `interests` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  CONSTRAINT `fk_interests_has_user_user1` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of interests_has_user
-- ----------------------------
INSERT INTO `interests_has_user` VALUES ('1', '1');
INSERT INTO `interests_has_user` VALUES ('2', '1');
INSERT INTO `interests_has_user` VALUES ('3', '1');
INSERT INTO `interests_has_user` VALUES ('4', '1');
INSERT INTO `interests_has_user` VALUES ('5', '1');

-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(45) DEFAULT NULL,
  `email` varchar(45) DEFAULT NULL,
  `password` varchar(45) DEFAULT NULL,
  `country` varchar(45) DEFAULT NULL,
  `state` varchar(45) DEFAULT NULL,
  `city` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES ('1', 'Name', 'email@email.com', '123123', '1', '1', '1');

我需要从 table[ 用户 ] 和 table[ interests_has_user]，用户可以在 table table[ interests_has_user ] 有很多兴趣，我就是这样查询的:

SELECT 
    user.id,
    user.name,
    user.email,
    user.country,
    user.state,
    user.city,
    interests_has_user.interests_id,
    interests_has_user.user_id
FROM 
    user
LEFT JOIN interests_has_user
ON user.id = interests_has_user.user_id
WHERE user.id = 1;

并且我抛出了tabletable[interests_has_user]的所有记录，但是在所有行中用户都是重复的，图片附上结果。

注意：黄色阴影部分应为空字段。

最好的解决方案是什么，使用 INNER JOIN，或者单独的consutas。

感谢您的帮助，非常感谢。

Answer 1

INNER JOIN 不会 return 没有兴趣的用户。所以这不是你想要的。如果你想减轻查询结果，你可以做两个查询：

首先找出用户详细信息

SELECT 
    user.id,
    user.name,
    user.email,
    user.country,
    user.state,
    user.city
FROM 
    user
WHERE user.id = 1

然后是兴趣id。

SELECT user.id, interests_has_user.interests_id, interests_has_user.user_id 
FROM user 
LEFT JOIN interests_has_user ON user.id = interests_has_user.user_id 
WHERE user.id = 1

MySQL - 删除重复记录实体关系多对多

MySQL - Remove duplicate records entity relationship many to many

database

relational-database