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Question

我有一个包含category和votes列的表格。我以前尝试过多种解决方案但收效甚微;通常会发生的是，不是返回每个类别中的前3个项目，而是返回所有可用项目。

SELECT `id`, `user_id`, `full_name`, `category`, `year`, `month`, `thumbnail_photo`, `photo_title`, `votes`
FROM
    (
    SELECT `id`, `user_id`, `full_name`, `category`, `year`, `month`, `thumbnail_photo`, `photo_title`, `votes`,
        @category_rank := IF(@current_category = category, @category_rank + 1, 1) AS category_rank,
        @current_category := category
    FROM `photo_contest`
    ORDER BY
        `category`,
        `votes` DESC
) ranked
WHERE
    category_rank <= 3
    AND `year` = '2017'
    AND `month` = 'April'
    AND `votes` > 0

此特定解决方案改编自SQLines。我最终想做的是转一个这样的表：

Name      | Category | Votes
--------- | -------- | -----
Name Foo  | CatFoo   | 0
Name Bar  | CatFoo   | 1
Name Baz  | CatFoo   | 10
Name Quux | CatFoo   | 200
Name ooF  | CatBar   | 50
Name raB  | CatBar   | 300
Name zaB  | CatBar   | 10
Name xuuQ | CatBar   | 200

...为：

Name      | Category | Votes
--------- | -------- | -----
Name Quux | CatFoo   | 200
Name Baz  | CatFoo   | 10
Name Bar  | CatFoo   | 1
Name raB  | CatBar   | 300
Name xuuQ | CatBar   | 200
Name ooF  | CatBar   | 50

...包含其他WHERE语句。年，月和最低票数。

Answer 1

您的子查询尝试计算整个表的排名。如果您只想使用投票＆gt;对所选年份进行排名0，您应该将这些条件作为自己的WHERE条件复制到子查询中。

更新：

看起来外部查询中缺少导致上述问题的struct IconSizes { var typesList: Array<String> var iphone: [Dictionary<String, Any>] init() { self.typesList = ["iPhone"] self.iphone = [ ["size":16,"name":"icon_small.png"], ["size":32,"name":"icon_small@2x.png"], ["size":32,"name":"icon_medium.png"], ["size":64,"name":"icon_medium@2x.png"], ["size":64,"name":"icon_large.png"], ["size":128,"name":"icon_large@2x.png"], ["size":128,"name":"icon.png"], ["size":256,"name":"icon@2x.png"] ] } } 。我在sqlfiddle创建了以下DDL / SQL。

ORDER BY

Answer 2

我不是MySQL的专家，所以我建议你使用不同的（标准SQL）方法：你可以在Category和Votes上加入表格，使其更少或相同到当前行的投票。

select  t1.Name, t1.Category, t1.Votes, count(distinct t2.Name) as rank
from    photo_contest t1
join    photo_contest t2
on      t1.Category = t2.Category and
        t1.Votes <= t2.Votes
/*where whatever you want*/
group by t1.Name, t1.Category, t1.Votes
having  count(distinct t2.Name) <= 3
order by t1.Category, rank

我测试了它here，它似乎做了你要求的

Answer 3

听起来您的PHPMyAdmin需要升级或替换。同时你可能想尝试@Stefano Zanini的非MySQL特定SQL：

SELECT
    t1.`id`, t1.`category`, t1.`year`, t1.`month`,
    t1.`votes`, count(distinct t2.`id`) as rank
FROM photo_contest t1
INNER JOIN photo_contest t2 ON
    t1.`category` = t2.`category` AND
    t1.`votes` <= t2.`votes`
WHERE t1.`votes` > 0
GROUP BY t1.`id`, t1.`category`, t1.`votes`
HAVING count(distinct t2.`id`) <= 3
ORDER BY t1.`category`, rank;

可在sqlfiddle上找到。如果您认为此解决方案更适合您，请将@Stefano Zanini的答案归功于此答案。