MySQL获取每个分类下面的前三条数据

DROP TABLE IF EXISTS `t_picture`;
CREATE TABLE `t_picture` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT COMMENT '主键Id号',
  `admin_id` int(11) NOT NULL DEFAULT '0' COMMENT '操作员id',
  `member_id` int(11) NOT NULL DEFAULT '0' COMMENT '用户id 与admin_id必须有一个为0',
  `admin_name` varchar(50) NOT NULL DEFAULT '' COMMENT '操作员名字',
  `title` varchar(100) NOT NULL DEFAULT '' COMMENT '图片标题',
  `name` varchar(255) NOT NULL DEFAULT '' COMMENT '图片名称',
  `ext` varchar(10) NOT NULL DEFAULT '' COMMENT '图片扩展名',
  `path` varchar(100) NOT NULL DEFAULT '' COMMENT '原图路径',
  `thumbnail_big_path` varchar(100) NOT NULL DEFAULT '' COMMENT '缩大图片路径',
  `thumbnail_small_path` varchar(100) NOT NULL DEFAULT '' COMMENT '缩小图片路径',
  `flag` int(4) unsigned NOT NULL DEFAULT '0' COMMENT '显示状态类型：1、显示2、隐藏',
  `add_time` int(11) unsigned NOT NULL DEFAULT '0' COMMENT '加添时间',
  `update_time` int(11) unsigned NOT NULL DEFAULT '0' COMMENT '修改时间',
  `album_id` int(11) NOT NULL DEFAULT '0' COMMENT '图片所在相册ID',
  `weight` tinyint(1) unsigned NOT NULL DEFAULT '0' COMMENT '权重，用于景点图片排序。253,254,255 作为预留值，用于3级置顶用。',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=29 DEFAULT CHARSET=utf8mb4 COMMENT='线路图片管理';

SELECT a.* FROM t_picture as a WHERE (SELECT COUNT(*) FROM t_picture as b WHERE b.album_id=a.album_id AND b.id>=a.id) <=3 ORDER BY a.album_id ASC,a.id DESC;

SELECT 
    a.*
FROM
    t_picture AS a,
    (SELECT 
        GROUP_CONCAT(id order by id desc) AS ids
    FROM
        t_picture
    GROUP BY album_id) AS b
WHERE
    FIND_IN_SET(a.id, b.ids) BETWEEN 1 AND 3
ORDER BY a.album_id ASC, a.id DESC;

select a.*,count(*) as num from t_picture as a inner join t_picture as b ON a.album_id=b.album_id where b.id>=a.id group by a.id having num<=3;