MySQL Select Where In Many to Many

问题

I'm having trouble with a SQL query. My schema describes a many to many relationship between articles in the articles table and categories in the categories table - with the intermediate table article_category which has an id, article_id and category_id field.

I want to select all articles which only have the categories with id 1 and 2. Unfortunately this query will also select any articles which have those categories in addition to any others.

For example, this is a sample output from the SQL (with categories shown for descriptive purposes). You can see that while the query selected the article with id of 10, it also selected the article with an id of 11 despite having one extra category.

+-------+------------+
| id    | categories |
+-------+------------+
| 10    | 1,2        |
| 11    | 1,2,3      |
+-------+------------+

This is the output that I want to achieve from selecting articles with only categories 1and 2.

+-------+------------+
| id    | categories |
+-------+------------+
| 10    | 1,2        |
+-------+------------+

Likewise, this is the output what I want to achieve from selecting articles with only categories 1, 2 and 3.

+-------+------------+
| id    | categories |
+-------+------------+
| 11    | 1,2,3      |
+-------+------------+

This is the SQL I have written. What am I missing to achieve the above?

SELECT articles.id
FROM articles
WHERE EXISTS (
    SELECT 1
    FROM article_category
    WHERE articles.id = article_id AND category_id IN (1,2)
    GROUP BY article_id
)

Many thanks!

回答1:

Assuming you want more than just the article's id:

SELECT a.id
      ,a.other_stuff
  FROM articles a
  JOIN article_category ac
    ON ac.article_id = a.id
GROUP BY a.id
HAVING GROUP_CONCAT(DISTINCT ac.category_id ORDER BY ac.category_id SEPARATOR ',') = '1,2'

If all you want is the article's id then try this:

SELECT article_id
  FROM article_category 
GROUP BY article_id
HAVING GROUP_CONCAT(DISTINCT category_id ORDER BY category_id SEPARATOR ',') = '1,2'

See it in action at http://sqlfiddle.com/#!2/9d213/4

Should also add that the advantage of this approach is that it can support the checking of any number of categories without having to change the query. Just make '1,2' a string variable and change what gets passed into the query. So, you could just as easily search for articles with categories 1, 2, and 7 by passing a string of '1,2,7'. No additional joins are needed.

回答2:

You can left join category_id on category.id and then GROUP_CONCAT to get all categories, like you wrote in explanation (1st table) and than using HAVING match with any set you like ( '1,2' from example)

also with that approach you can easily make this query dynamic with php or any other language

SELECT articles.id
FROM articles
WHERE EXISTS (
    SELECT GROUP_CONCAT(c.id) AS grp
    FROM article_category
    LEFT OUTER JOIN categories AS c ON c.id = article_category.category_id
    WHERE articles.id = article_id
    GROUP BY article_id
    HAVING grp = '1,2'
)

回答3:

Please Use Below Query You can do the Thing by Using Simple Query.

   SELECT a.id, a.name
    FROM articles a, categories c, articles_categories ac 
    WHERE
    a.id = ac.article_id AND c.id = ac.category_id 
    AND c.id = 1 OR c.id = 2;

NOTE- If You have Many to many Relationship between two Tables Remove ID from the article_category table and make composite primary key Using article_id and category_id.

Thank you.

回答4:

Maybe, something like:

select distinct article_id from article_cathegory 
      where category_id in (1,2)
minus 
select distinct article_id from article_cathegory 
      where category_id not in (1,2)

回答5:

Looks like simple solution for this could be the following:

SELECT 
    ac.article_id
    , SUM(ac.category_id IN (1, 2)) AS nb_categories
    , COUNT(ac.category_id) AS nb_all_categories
FROM
    article_categories ac
GROUP BY
    ac.article_id
HAVING
    nb_categories=2 AND nb_all_categories=2

Here I count how many required categories we have and also count how many categories we have in total. We only need exactly 2 categories, so both required and total should be equal to 2.

This is quite flexible and for adding more categories just change categories list and numbers in HAVING statement.

回答6:

SELECT articles.id
FROM articles
INNER JOIN articles_category ac ON articles.id = ac.article_id
WHERE articles.id IN (
     SELECT ac1.article_id
     FROM article_category ac1
     WHERE ac1.category_id = 1;
     )
AND ac.article_id = 2;
AND articles.id NOT IN (
     SELECT ac2.article_id
     FROM article_category ac2
     WHERE ac2.category_id NOT IN (1, 2)
     )

Far from the prettiest one I have written.

Basically, it limits first by ID that have a category id of 1, then it makes sure the records have a category of 2 as well, finally, it makes sure that it does not have any other categories

回答7:

I like to approach these queries using group by and having. Here is an example:

select ac.article_id
from article_category ac
group by ac.article_id
having sum(case when category_id = 1 then 1 else 0 end) > 0 and
       sum(case when category_id = 1 then 2 else 0 end) > 0;

Each condition in the having clause is testing for the presence of one of the categories.

I find that this approach is the most flexible for answering many different types of "set-within-sets" problems.

EDIT:

A slight variation on the above might be easier to generate:

having sum(category_id in (1, 2, 3)) = count(*) and
       count(*) = 3

This will work assuming there are no duplicates in the data. You need to update the 3 to be the number of items in the in list.

回答8:

to help just without changing your query very much, i think the logic has a bug. you dont want articles where a categegory 1,2 exists. You need articles where does not exist categories different than 1 and 2. thanks & regards

回答9:

In SQL Server I would do it with an INTERSECT and an EXCEPT. In MySQL, try this:

SELECT DISTINCT article_id
  FROM article_category
  WHERE category_id=1
AND article_id IN
(SELECT article_id
  FROM article_category
  WHERE category_id=2)
AND article_id NOT IN
(SELECT article_id
  FROM article_category
  WHERE category_id NOT IN (1,2))

回答10:

Use this SQL query.

SELECT articles.id
FROM articles
WHERE articles.id in (
    SELECT *
    FROM article_category,articles
    WHERE article_category.articles.id = articles.article_id AND article_category.category_id IN (1,2)
)

来源：https://stackoverflow.com/questions/23231549/mysql-select-where-in-many-to-many

标签

mysql

sql

many-to-many