MySQL查询：使用非唯一值排序列表时，获取下一个或上一个项目

Question

我有图像库。每张图片的评分都是基于有多少用户投票“我喜欢这个”。 MySQL表的这种笑话是这样的：

id  |image  |rating 
------------------------------------ 
166  |6.png  |9 
165  |8.png  |9 
189  |1.png  |8 
171  |99.png  |8 
169  |56.png  |8 
155  |34.png  |8 
265  |7.png  |7 
754  |86.png  |6 
166  |37.png  |4 
342  |95.png  |2 
99  |35.png  |0 
76  |34.png  |0 
44  |3.png  |0 
8  |22.png  |0 

任务是：可以查看按评级排序的画廊。使用ORDER BY rating DESC, id DESC很容易列出图像，但用户点击图像时出现问题，我必须在打开的图像旁边显示“上一张图像”和“下一张图像”按钮。

假设我们现在看到的与示例表ID = 169的图像：

id  |image  |rating 
------------------------------------ 
169  |99.png  |8 

我怎么能写我的查询，以获得一张图像（ID = 171）？问题是，主要排序是rating（这不是唯一的）和次要是由唯一的id。在任何情况下，哪个查询都会给我正确的以前的图像。

我已经试过：

SELECT * 
FROM images 
WHERE rating >= 8 AND id >=169 
ORDER BY rating, id 
LIMIT 1 

，但它并没有这样做，因为id >=169必须检查只有等级相同。

我有点困惑，请帮助我。

UPDATE

想通了这一个我自己。假设我对当前记录的rating和id值，查询得到此前的纪录是：

SELECT * 
FROM `images` 
WHERE 
    (`rating` = 8 AND `id` > 169) 
    OR `rating` > 8 
ORDER BY `rating`, `id` 
LIMIT 1 

如果rating = 8 AND id > 169没有评估，然后rating > 8进入游戏。原来很简单。

谢谢大家！接受大多数赞成的答案。

Answer 1

SELECT * FROM images ORDER BY rating DESC, id LIMIT $n, 1 

其中$n是ID从0开始订购计数器可以确保后续调用始终保持相同的顺序。因此下一张图片将是$n+1，之前的$n-1。

此外，如果您想要确保当前存在下一张图片（用户当然不喜欢点击“下一个”以获取404错误），您总是可以抓取2张图片。

编辑：从评论

嗯了新的要求，你可以尝试计算最小距离你当前的图像。

SELECT * from images 
WHERE id < $current[id] AND rating >= $current[rating] 
ORDER by ((abs($current[rating] - rating) << 32) + abs($current[id] - id)) 
LIMIT 1 

SELECT * from images 
WHERE id > $current[id] AND rating <= $current[rating] 
ORDER by ((abs($current[rating] - rating) << 32) + abs($current[id] - id)) 
LIMIT 1 

不要问我任何性能虽然;）

Answer 2

获取一个查询中的所有条目，将其放入一个php数组中，然后使用它来代替！

Answer 3

您正在寻找一种面向游标的方法。另一个非常简单的方法是通过特定的排序条件选择所有ID，将它们保存在应用程序中，然后使用ID和查询进行浏览和选择，具体选择所需的行。

Answer 4

试试这一个，更换test你的表名和更换curr.id =169当前页ID

SELECT curr.id AS currid, curr.image as curr_img, 
      prev.id AS previd, prev.image as prev_img, 
      next.id AS nextid, next.image as next_img 
    FROM test curr 
    LEFT JOIN test prev 
     ON prev.id != curr.id 
     AND (
      prev.rating > curr.rating 
      OR (
       prev.rating = curr.rating 
       AND prev.id > curr.id 
     ) 
     ) 
    LEFT JOIN test next 
     ON next.id != curr.id 
     AND (
      next.rating < curr.rating 
      OR (
        next.rating = curr.rating 
        AND next.id < curr.id 
      ) 
     ) 
    WHERE curr.id =169 
    ORDER BY prev.rating ASC , next.rating DESC , prev.id ASC , next.id DESC 
    LIMIT 1 

Answer 5

我记得一篇我在MySQL性能博客上阅读的关于pagination的文章，并敲起了这个例子，这可能会有帮助（@row_id是多余的）

drop table if exists gallery; 
create table gallery 
(
id int unsigned not null, 
image varchar(255) not null, 
rating tinyint unsigned default 0 
) 
engine=innodb; 

insert into gallery values 
(166,'6.png',9),(165,'8.png',9),(189,'1.png',8), 
(171,'99.png',8),(169,'56.png',8),(155,'34.png',8), 
(265,'7.png',7),(754,'86.png',6),(37,'37.png',4), 
(342,'95.png',2),(99 ,'35.png',0),(76 ,'34.png',0), 
(44 ,'3.png',0),(8 ,'22.png',0), (1001 ,'1001.png',0); 

drop procedure if exists list_gallery_paged; 

delimiter # 

create procedure list_gallery_paged 
(
in p_last_id int unsigned, 
in p_last_rating tinyint unsigned 
) 
proc_main:begin 

    set @row_id = 0; 

    if p_last_id <= 0 then 
     select @row_id:=@row_id+1 as row_id, g.* 
     from gallery g order by rating desc, id desc limit 4; 
    else 
     select @row_id:=@row_id+1 as row_id, g2.* 
     from gallery g inner join gallery g2 on g.id = g2.id 
     where 
     g.rating <= p_last_rating and (g.id < p_last_id or g.rating < p_last_rating) 
     order by 
     g.rating desc, g.id desc limit 4; 
    end if; 

end proc_main # 

delimiter ; 

-- in pages of 4 (use all rows) 
select g.* from gallery g order by rating desc, id desc; 
call list_gallery_paged(0,0); 
call list_gallery_paged(171,8); 
call list_gallery_paged(754,6); 
call list_gallery_paged(99,0); 
call list_gallery_paged(8,0); 

-- one at a time (use top row only) 
select g.* from gallery g order by rating desc, id desc; 
call list_gallery_paged(265,7); 
call list_gallery_paged(754,6); 
call list_gallery_paged(37,4); 
call list_gallery_paged(342,2); 
call list_gallery_paged(1001,0); 
call list_gallery_paged(99,0); 
call list_gallery_paged(76,0); 
call list_gallery_paged(44,0); 
call list_gallery_paged(8,0);