媒体表：

CREATE TABLE $media_table (
            `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
            `title` varchar(300) DEFAULT NULL,
            `options` longtext DEFAULT NULL,
            PRIMARY KEY (`id`)
}

表格示例：

id    title     options
--------------------------
1     video      ...         
2     video      ...         
3     audio      ...

类别表：

CREATE TABLE $media_taxonomy_table ( 
            `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
            `type` varchar(15) DEFAULT NULL,
            `title` varchar(300) DEFAULT NULL,
            `media_id` int(11) unsigned DEFAULT NULL,
            PRIMARY KEY (`id`),
            INDEX `media_id` (`media_id`)
}

类型可以是“category”或“tag”（我猜这可能是enum）
表格示例：

id    type         title      media_id
---------------------------------------
1     category      rock         1  
2     category      trance       1 
3     category      trance       2 
4     category      rock         3
5     tag           silent       1
5     tag           loud         1
6     tag           foo          2

我正在尝试从$media\u taxonomy\u表中对\u concat的category和tag进行分组。
此查询将返回只有类别的组\u concat

SELECT mt.id, mt.title, mt.options, GROUP_CONCAT(mtt.title ORDER BY mtt.title ASC SEPARATOR ', ') as category 
    FROM $media_table as mt
    LEFT JOIN $media_taxonomy_table as mtt 
    ON mt.id = mtt.media_id AND mtt.type='category'
    WHERE playlist_id = %d 
    GROUP BY mt.id

结果，收到：

id    title         options     category
----------------------------------------
1     video           ...       rock, trance  
2     video           ...       trance  
3     audio           ...       rock

预期（我也需要标签）：

id    title         options     category          tag
--------------------------------------------------------------
1     video           ...       rock, trance      silent, load
2     video           ...       trance            foo
3     audio           ...       rock