MySQL Query for Tagging System, Selecting Used Tags Only

I have a tagging system implemented in PHP and MySQL, with the following tables:

Table: blog_t开发者_开发技巧ags

• tag_id
• tag_name

Table: blog_tags_assoc

• tag_assoc_id
• article_id
• tag_id

Table: blog_articles

• article_id
• article_title
• article_content

I have them all linked using the Many to Many relationship (reference to something similar: How to store tags in MySQL tags, one field in total or one filed for each tag?)

What I'm trying to do now is make a MySQL query that selects all the tags from blog_tags that have actually been referenced by the articles in blog_articles.

So far, I know that "HAVING" is something I might use…but I'm not sure how? Any ideas or suggestions would be most welcome. Thanks!

If you only want to know the tags that have been used in articles, then you can simply do this:

SELECT DISTINCT tag_id, tag_name
FROM blog_tags
INNER JOIN blog_tags_assoc USING ( tag_id );

This will get a tag name as well as a count of articles that tag has been used.

SELECT
    `blog_tags`.`tag_name`,
    count(*) AS `blog_article_count`
FROM `blog_tags`
    JOIN `blog_tags_assoc`
        ON `blog_tags`.`tag_id`=`blog_tags_assoc`.`tag_id`
    JOIN `blog_articles`
        ON `blog_articles`.`article_id`=`blog_tags_assoc`.`article_id`
GROUP BY `blog_tags`.`tag_name`