blocks|key|1375271|text|如果没有任何唯一约束，请尝试：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1375272|SELECT+post_id+
FROM+tags+
WHERE+tag_id+=+1+OR+tag_id+=+3+
GROUP+BY+post_id+
HAVING+count(DISTINCT+tag_id)+=+2;|code-block|syntax|javascript|1375273|如果尝试仅检测两个tag_id值，则使用此HAVING子句：|offset|length|style|CODE|1375274|HAVING+MIN(tag_id)+<>+MAX(tag_id)|1375275|如果post_id和tag_id都有一个唯一的约束，这也应该是可行的：|1375276|SELECT+post_id+
FROM+tags+
WHERE+tag_id+=+1+OR+tag_id+=+3+
GROUP+BY+post_id+
HAVING+count(*)+=+2;|1375277|entityMap^0|0|0|9|6|L|6|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@$I|X|J|Y|K|L]|$I|Z|J|10|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|12|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|S|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|T|$]]

If there aren't any unique constraints try:

<pre><code>SELECT post_id 
FROM tags 
WHERE tag_id = 1 OR tag_id = 3 
GROUP BY post_id 
HAVING count(DISTINCT tag_id) = 2;
</code></pre>

Or use this <code>HAVING</code> clause, if trying to detect only two <code>tag_id</code> values:

<pre><code>HAVING MIN(tag_id) &lt;&gt; MAX(tag_id)
</code></pre>

If post_id and tag_id both have an unique constraint, this should work too:

<pre><code>SELECT post_id 
FROM tags 
WHERE tag_id = 1 OR tag_id = 3 
GROUP BY post_id 
HAVING count(*) = 2;
</code></pre>

blocks|key|628963|text|您可以尝试自连接(N+tag_id+->+N+join)，但它可能不快|type|unstyled|depth|inlineStyleRanges|entityRanges|data|628964|SELECT+t1.post_id+
FROM+tags+t1+INNER+JOIN+tags+t2+ON+t1.post_id+=+t2.post_id+
WHERE+t1.tag_id+=+1+AND+t2.tag_id+=+3|code-block|syntax|javascript|628965|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You could try a self join (N tag_id -> N join) but probably it's not fast

<pre><code>SELECT t1.post_id 
FROM tags t1 INNER JOIN tags t2 ON t1.post_id = t2.post_id 
WHERE t1.tag_id = 1 AND t2.tag_id = 3
</code></pre>

blocks|key|3627642|text|SELECT+post_id
++FROM+(+SELECT+post_id,
++++++++++++++++count(tag_id)+AS+counter
+++++++++++FROM+tags
++++++++++WHERE+tag_id+IN+(1,3)
++++++++++GROUP+BY+post_id
+++++++)
+WHERE+counter+=+2|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3627643|对问题的第二部分使用GROUP_CONCAT()|unstyled|3627644|SELECT+post_id,
+++++++GROUP_CONCAT(tag_id+ORDER+BY+tag_id+ASC+SEPARATOR+',')
++FROM+tags|3627645|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|I|3|-4|5|F|7|N|8|@]|9|@]|A|$]]]|J|$]]

<pre><code>SELECT post_id
 FROM ( SELECT post_id,
 count(tag_id) AS counter
 FROM tags
 WHERE tag_id IN (1,3)
 GROUP BY post_id
 )
 WHERE counter = 2
</code></pre>

Use GROUP_CONCAT() for the second part of your question

<pre><code>SELECT post_id,
 GROUP_CONCAT(tag_id ORDER BY tag_id ASC SEPARATOR ',')
 FROM tags
</code></pre>

blocks|key|628951|text|我对您的其他表做了一些假设。(例如，您有一个我称为posts的帖子表和一个以tag_id作为PK的表，我将其称为tag_table，以避免与posts/tags表的名称冲突，我可以看到您已经调用了tags)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|628952|您希望在列表{1,3}中不存在标签的帖子，也不存在与相应post_id/+tag+_id匹配的记录，因此您可以使用double+not+EXISTS结构，如下所示。|628953|SELECT+post_id
FROM+posts+p
WHERE+NOT+EXISTS+
++++(SELECT+*+FROM+tag_table+tt
++++WHERE+tag_id+IN+(1,3)
++++AND+NOT+EXISTS
++++++++(SELECT+*+FROM+tags+t
++++++++WHERE+t.tag_id+=+tt.tag_id++and
++++++++p.post_id+=+t.post_id)++++++++
++++)|code-block|syntax|javascript|628954|另一种替代方法是使用Group+By和Count。A+review+of+approaches+to+this+problem+is+here。|628955|entityMap|0|LINK|mutability|MUTABLE|url|http://www.simple-talk.com/sql/t-sql-programming/divided-we-stand-the-sql-of-relational-division/^0|P|5|1K|9|2Q|4|0|0|0|P|1A|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|14|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|15|8|@]|D|@$9|16|A|17|1|18]]|E|$]]|$1|O|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

I've made some assumptions about your other tables. (i.e. that you have a table for posts that I have called <code>posts</code> and one with tag_id as the PK which I have called <code>tag_table</code> to avoid a nameclash with the posts/tags table that I can see you already call <code>tags</code>) 

You want posts where there does not exist a tag in the list {1,3} for which there does not exist a matching record with the corresponding post_id/tag_id so you can use a double NOT EXISTS construct as below.

<pre><code>SELECT post_id
FROM posts p
WHERE NOT EXISTS 
 (SELECT * FROM tag_table tt
 WHERE tag_id IN (1,3)
 AND NOT EXISTS
 (SELECT * FROM tags t
 WHERE t.tag_id = tt.tag_id and
 p.post_id = t.post_id) 
 )
</code></pre>

Another alternative approach is to use Group By and Count. <a href="http://www.simple-talk.com/sql/t-sql-programming/divided-we-stand-the-sql-of-relational-division/" rel="nofollow noreferrer">A review of approaches to this problem is here</a>.

blocks|key|1371647|text|怎么样|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1371648|SELECT+*+
FROM+tags+
WHERE+post_id+in+
++(SELECT+post_id+AS+pid+
+++FROM+tags+
+++WHERE+1+IN+(SELECT+tag_id+FROM+tags+WHERE+post_id+=+pid)+
+++AND+3+IN+(SELECT+tag_id+FROM+tags+WHERE+post_id+=+pid)
++);|code-block|syntax|javascript|1371649|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

How about

<pre><code>SELECT * 
FROM tags 
WHERE post_id in 
 (SELECT post_id AS pid 
 FROM tags 
 WHERE 1 IN (SELECT tag_id FROM tags WHERE post_id = pid) 
 AND 3 IN (SELECT tag_id FROM tags WHERE post_id = pid)
 );
</code></pre>

blocks|key|628983|text|@Keeper的解决方案的版本|type|unstyled|depth|inlineStyleRanges|entityRanges|data|628984|SELECT+DISTINCT+t1.post_id+
FROM+tags+t1,+tags+t2
WHERE+
++t1.post_id+=+t2.post_id++AND+
++t1.tag_id+=+1+AND+t2.tag_id+=+3|code-block|syntax|javascript|628985|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

WHERE version of @Keeper's solution

<pre><code>SELECT DISTINCT t1.post_id 
FROM tags t1, tags t2
WHERE 
 t1.post_id = t2.post_id AND 
 t1.tag_id = 1 AND t2.tag_id = 3
</code></pre>

Say there is such table:

<pre><code>mysql&gt; SELECT * FROM tags;
+---------+--------+
| post_id | tag_id |
+---------+--------+
| 1 | 2 |
| 1 | 3 |
| 1 | 1 |
| 2 | 1 |
| 2 | 2 |
+---------+--------+
5 rows in set (0.00 sec)
</code></pre>

Field names are pretty self-explanatory. I want to select <code>post_id</code>s that have both 1 and 3 <code>tag_id</code>s, so in this example it's only <code>1</code>. I thought of something like 
<code>SELECT post_id FROM tags GROUP BY post_id HAVING ...</code> After having I'd like to list <code>tag_id</code>s that are present in this group. How do I do that?

Mysql: how to select groups having certain values?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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假设有这样一张表：mysql> SELECT * FROM tags;+---------+--------+| post_id | tag_id |+---------+--------+|       1 |      2 ||       1 |      3 ||       1 |      1 ||       2 |      1 ||       2 |      2 |+----

问Mysql:如何选择具有特定值的分组？
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问Mysql:如何选择具有特定值的分组？
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