Question

This is relating to my last question mysql query with AND, OR and NOT

Instead of editing the question, I am asking a new one because the question is only part of the previous question with an alteration.

I am looking to do a mysql query that returns me all articles that have all required topics.

Article
   id
   ....

Topic
   id
   ....

ArticleTopics
   article_id
   topic_id
   type

something that would effectively do:

SELECT * FROM Article LEFT JOIN ArticleTopics ON Article.id = ArticleTopics.article_id
WHERE ArticleTopics.topic_id HAS ALL (these topics)

Is this possible? What is the best approach for this?

Answer 1

Several of the other answers suggest using aliases on the child table for each filter clause – this may not be very efficient or scale well.

Consider:

SELECT x.*
FROM Article x INNER JOIN
(SELECT t.article_id, COUNT(t.article_id)
  FROM articleTopics t
  WHERE t.topic_id IN ([your_list_of_topics])
  GROUP BY t.article_id
  HAVING COUNT(t.article_id)>=[number of elements in [your_list_of_topics]]
  ORDER BY COUNT(t.article_id) DESC
  LIMIT 0,100) AS ilv
ON x.id=ilv.article_id

Another advantage of this approach is that the structure of the query doesn’t need to change with the number of topics you are searching for – you could even put them in a temporary table and perform a join instead of using the ‘ IN (…)’ literal.

You’d need to try it out to see which query behaves better.