题
我有一些麻烦一个棘手的SQL-查询。
在我数据库里发表的主题、标签和tags_topics加入他们。我想要取一些主题,分享相同的指定标签。例如,让我们说有3个标签与id1、2和3中,我想提取的所有主题,有标签的标1、2和3相关联。主题可以有其他的标签,但是必须有所有指定的标记。
帮我想想。。
编辑:找到一个解决方案使用组通过在这个问题: 获取行匹配的所有条目中加入了表(SQL) 如果任何人有一个更优雅的方案,请后:)
解决方案
<强> JOIN
溶液强>
SELECT t.*
FROM topics t
JOIN tags_topics t1 ON (t.id = t1.topicId AND t1.tagId = 1)
JOIN tags_topics t2 ON (t.id = t2.topicId AND t2.tagId = 2)
JOIN tags_topics t3 ON (t.id = t3.topicId AND t3.tagId = 3)
<强> GROUP BY
溶液强>
请注意,你需要列出t.*
子句中的所有列GROUP BY
,除非你使用MySQL或SQLite的。
SELECT t.*
FROM topics t JOIN tags_topics tt
ON (t.id = tt.topicId AND tt.tagId IN (1,2,3))
GROUP BY t.id, ...
HAVING COUNT(*) = 3;
<强>子查询的解决方案:强>
SELECT t.*
FROM topics t
WHERE t.id = ANY (SELECT topicId FROM tags_topics tt WHERE tt.tagId = 1)
AND t.id = ANY (SELECT topicId FROM tags_topics tt WHERE tt.tagId = 2)
AND t.id = ANY (SELECT topicId FROM tags_topics tt WHERE tt.tagId = 3);
<强>改性GROUP BY
溶液强>
通过在子查询中分离搜索简化GROUP BY
子句。
SELECT t.*
FROM topics t
WHERE t.id IN (
SELECT tt.topicId FROM tags_topics tt
WHERE tt.tagId IN (1,2,3))
GROUP BY tt.id HAVING COUNT(*) = 3
);
其他提示
SELECT
topic_id
FROM
tags_topics
WHERE
tag_id IN (1,2,3)
GROUP BY
topic_id
HAVING
COUNT(*) > 2 /* or use COUNT(*) = 3 if you know that there cannot be duplicates in the junction table */
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