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  • mysql中GROUP_CONCAT的使用

    现在有三个表,结构如下:
    cate表
    CREATE TABLE `cate` (
      `id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT 'id',
      `name` char(20) DEFAULT '' COMMENT '分类名',
      PRIMARY KEY (`id`)
    ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 COMMENT='文章分类表';
    
    article表
    CREATE TABLE `article` (
      `id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT 'id',
      `title` varchar(50) DEFAULT '',
      `cate_id` int(11) NOT NULL DEFAULT '0' COMMENT '分类id',
      PRIMARY KEY (`id`)
    ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 COMMENT='文章表';
    
    article_extend表
    CREATE TABLE `article_extend` (
      `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
      `article_id` int(10) unsigned DEFAULT '0' COMMENT '文章id',
      `name` varchar(255) DEFAULT '' COMMENT '音频,图片之类',
      PRIMARY KEY (`id`)
    ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 COMMENT='附件表';
    三张表数据如下:
    cate表:
     article表:
     article_extend表:
    问题来了,现在通过表连接查询,查询文章id为1的文章数据,并显示文章标题,文章分类,文章name。
    SELECT
    	a.id AS aid,
    	a.title AS atitle,
    	c. NAME AS cname,
    	ae. NAME AS aname
    FROM
    	article AS a
    LEFT JOIN cate AS c ON a.cate_id = c.id
    LEFT JOIN article_extend AS ae ON a.id = ae.article_id
    WHERE
    	a.id = 1;
    
    结果如下,出现了两条数据:
    现在只想要一条结果,aname字段进行合并,如何做?
    只有通过GROUP_CONCAT来实现了:
    SELECT
    	a.id AS aid,
    	a.title AS atitle,
    	c. NAME AS cname,
    	GROUP_CONCAT(ae. NAME SEPARATOR '-') AS aname
    FROM
    	article AS a
    LEFT JOIN cate AS c ON a.cate_id = c.id
    LEFT JOIN article_extend AS ae ON a.id = ae.article_id
    WHERE
    	a.id = 1;
    
    结果如下:
    那么,现在我们不想通过文章id一条一条的查,我们要取全部,但如果文章name有多个的要进行合并,如何做?
    SELECT
    	a.id AS aid,
    	a.title AS atitle,
    	c. NAME AS cname,
    	ae.allname
    FROM
    	article AS a
    LEFT JOIN (
    	SELECT
    		ae.article_id,
    		GROUP_CONCAT(ae. NAME) AS allname
    	FROM
    		article_extend AS ae
    	GROUP BY
    		ae.article_id
    ) AS ae ON a.id = ae.article_id
    LEFT JOIN cate AS c ON a.cate_id = c.id;
    
    结果如下:
     
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  • 原文地址:https://www.cnblogs.com/jkko123/p/6294718.html
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