MYSQL实现列拼接，即同一个字段，多条记录拼接成一条

一、首先，新建三张表

DROP TABLE IF EXISTS `article`;
CREATE TABLE `article` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `title` varchar(255) NOT NULL COMMENT \'标题\',
  `content` text NOT NULL COMMENT \'内容\',
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 COMMENT=\'文章表\';

-- ----------------------------
-- Records of article
-- ----------------------------
INSERT INTO `article` VALUES (\'1\', \'标题1\', \'内容1\');
INSERT INTO `article` VALUES (\'2\', \'标题2\', \'内容2\');
INSERT INTO `article` VALUES (\'3\', \'标题3\', \'内容3\');
INSERT INTO `article` VALUES (\'4\', \'标题4\', \'内容4\');

-- ----------------------------
-- Table structure for article_tag
-- ----------------------------
DROP TABLE IF EXISTS `article_tag`;
CREATE TABLE `article_tag` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `article_id` int(10) unsigned NOT NULL COMMENT \'文章ID\',
  `tag_id` int(10) unsigned NOT NULL COMMENT \'标签ID\',
  PRIMARY KEY (`id`),
  KEY `idx_tag_id` (`tag_id`) USING BTREE,
  KEY `idx_article_id` (`article_id`) USING BTREE
) ENGINE=MyISAM AUTO_INCREMENT=13 DEFAULT CHARSET=utf8 COMMENT=\'文章-标签关联表\';

-- ----------------------------
-- Records of article_tag
-- ----------------------------
INSERT INTO `article_tag` VALUES (\'1\', \'1\', \'1\');
INSERT INTO `article_tag` VALUES (\'2\', \'1\', \'2\');
INSERT INTO `article_tag` VALUES (\'3\', \'1\', \'3\');
INSERT INTO `article_tag` VALUES (\'4\', \'1\', \'4\');
INSERT INTO `article_tag` VALUES (\'5\', \'2\', \'2\');
INSERT INTO `article_tag` VALUES (\'6\', \'2\', \'3\');
INSERT INTO `article_tag` VALUES (\'7\', \'2\', \'4\');
INSERT INTO `article_tag` VALUES (\'8\', \'3\', \'1\');
INSERT INTO `article_tag` VALUES (\'9\', \'3\', \'3\');
INSERT INTO `article_tag` VALUES (\'10\', \'4\', \'1\');
INSERT INTO `article_tag` VALUES (\'11\', \'4\', \'2\');
INSERT INTO `article_tag` VALUES (\'12\', \'4\', \'4\');

-- ----------------------------
-- Table structure for tag
-- ----------------------------
DROP TABLE IF EXISTS `tag`;
CREATE TABLE `tag` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `tag_name` varchar(255) NOT NULL COMMENT \'标签名\',
  `tag_desc` varchar(255) NOT NULL COMMENT \'标签注释\',
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 COMMENT=\'标签表\';

-- ----------------------------
-- Records of tag
-- ----------------------------
INSERT INTO `tag` VALUES (\'1\', \'tag1\', \'标签1\');
INSERT INTO `tag` VALUES (\'2\', \'tag2\', \'标签2\');
INSERT INTO `tag` VALUES (\'3\', \'tag3\', \'标签3\');
INSERT INTO `tag` VALUES (\'4\', \'tag4\', \'标签4\');

二、接下来查询关联关系

SELECT
    t1.*,tag_name,tag_desc
FROM
    `article` t1
LEFT JOIN article_tag t2 ON t1.id = t2.article_id
LEFT JOIN tag t3 ON t2.tag_id = t3.id

这是我们正常查询得到的结果，但实际上我们一般是想要把文章id相同的当做同一条记录，至于标签信息，我们也希望把它们合并到一起，在同一个字段展示，如右图所示

                

 

三、我们可以通过使用GROUP_CONCAT()函数来得到这种结果

SELECT
    t1.*,GROUP_CONCAT(tag_name) tag_name,GROUP_CONCAT(tag_desc) tag_desc
FROM
    `article` t1
LEFT JOIN article_tag t2 ON t1.id = t2.article_id
LEFT JOIN tag t3 ON t2.tag_id = t3.id
GROUP BY t1.id