[英]MySQL: Display one random result which a user has not voted on
I need help on displaying one random result in which the current user has not voted on. 我需要帮助显示当前用户尚未投票的随机结果。
Currently my database setup and the last query I have tried can be found on http://sqlfiddle.com/#!2/2f91b/1 目前我的数据库设置和我尝试的最后一个查询可以在http://sqlfiddle.com/#!2/2f91b/1找到
Basically I can isolate each individual item using this query: 基本上我可以使用此查询隔离每个单独的项目:
SELECT a.img_url, a.item_id, a.user_id, a.img_status, b.item_question, c.user_name, c.user_fbid, d.voter_id, count(d.img_id) AS totalVotes
FROM os_photos a
LEFT JOIN os_items b ON a.item_id = b.item_id
LEFT JOIN os_users c ON a.user_id = c.user_id
LEFT JOIN os_votes d ON a.img_id = d.img_id
GROUP BY a.img_id
ORDER BY RAND()
LIMIT 1
My Problem is: With the SQL knowledge that I have, I am unable to isolate the results to show only the rows in which user #2 has not voted on. 我的问题是:凭借我拥有的SQL知识,我无法隔离结果以仅显示用户#2未投票的行。 I realize the problem is when I use group by, it combines the voter_id and therefore I am unable to check if user #2 has had any input for the item.
我意识到问题是当我使用group by时,它结合了voter_id,因此我无法检查用户#2是否有任何项目输入。
Example: 例:
Item # | voter_id
1 | 2
1 | 3
2 | 2
3 | 1
3 | 4
4 | 3
4 | 1
5 | 1
5 | 2
With the above sample set, the resulting item should be either item #3, #4 or any other items which have not been voted on. 使用上面的样本集,结果项应该是项目#3,#4或任何其他尚未投票的项目。
Your help, advise and knowledge is greatly appreciated. 非常感谢您的帮助,建议和知识。
To get the items that dont exist you need a LEFT JOIN
with condition that would otherwise make a positive match, and then add a WHERE
clause matching one of the resulting columns to NULL
: 要获取不存在的项,您需要
LEFT JOIN
,条件否则会产生正匹配,然后添加一个WHERE
子句,将其中一个结果列与NULL
匹配:
SELECT a.img_url, a.item_id, a.user_id, a.img_status, b.item_question, c.user_name,c.user_fbid, d.voter_id, count(d.img_id) AS totalVotes
FROM os_photos a
LEFT JOIN os_items b ON a.item_id = b.item_id
LEFT JOIN os_users c ON a.user_id = c.user_id
LEFT JOIN os_votes d ON a.img_id = d.img_id
LEFT JOIN os_votes d2 ON a.img_id = d2.img_id AND d2.voter_id=2
WHERE d2.voter_id IS NULL
GROUP BY a.img_id
ORDER BY RAND()
LIMIT 1
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