mysql中GROUP_CONCAT的使用方法实例分析

本文实例讲述了mysql中group_concat的使用方法。分享给大家供大家参考，具体如下：

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：