MYSQL實現列拼接，即同一個字段，多條記錄拼接成一條

一、首先，新建三張表

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

-- ----------------------------
-- Records of article
-- ----------------------------
INSERT INTO `article` VALUES ('1', '標題1', '內容1');
INSERT INTO `article` VALUES ('2', '標題2', '內容2');
INSERT INTO `article` VALUES ('3', '標題3', '內容3');
INSERT INTO `article` VALUES ('4', '標題4', '內容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 '標簽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-標簽關聯表';

-- ----------------------------
-- 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 '標簽名',
  `tag_desc` varchar(255) NOT NULL COMMENT '標簽注釋',
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 COMMENT='標簽表';

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

二、接下來查詢關聯關系

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

這是我們正常查詢得到的結果，但實際上我們一般是想要把文章id相同的當做同一條記錄，至於標簽信息，我們也希望把它們合並到一起，在同一個字段展示，如右圖所示

                

 

三、我們可以通過使用GROUP_CONCAT()函數來得到這種結果

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