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：
