Question

My goal is to select articles where the primary_category_id (articles table) or any of the
secondary categories (articles_secondary_categories join table) are a given value. In this example query, category 1. I tried using other types of joins but the caveat here is that an article might not have any secondary categories.

SELECT DISTINCT articles.* 
FROM articles
LEFT JOIN articles_secondary_categories AS categories 
    ON categories.article_id = articles.id
WHERE 
(
    primary_category_id = 1
    OR
    categories.category_id = 1
)
    AND articles.state = "published"
    AND edition_id = 1

ORDER BY publish_at DESC
LIMIT 10;

Any help optimizing this or alternatives are welcome. In a DB with 4k articles and 7k articles_secondary_categories (not categories) it takes 5 seconds to run this query.

Answer 1

You can reverse the query on the secondary categories:

(SELECT articles.* 
FROM articles
WHERE primary_category_id = 1)
UNION DISTINCT
(SELECT articles.*
FROM articles_secondary_categories AS categories 
JOIN articles ON (categories.article_id = articles.id)
WHERE categories.category_id = 1
GROUP BY articles_id)
ORDER BY publish_at DESC
LIMIT 10;

It should give you a decent speed boost – just make sure you index categories.articles_id