Question

I have a news section. Articles are tagged and stored in 3 tables:

posts:

posts_id,title,body

tags:

tags_id,name

posts_tags:

posts_id,tags_id

The problem at the moment is that the front page of the news section displays previews of the first 10 articles. Each preview displays the tag lists. Displaying the tag lists means I have to query again for each post to get a list of the tags.

So for example, the 10 previews requires, 1 query(gets 10 posts from posts)+10 queries(1 for each post on tags and posts_tags to get tag lists). 11 queries to load a page seems like it could eventually be a bottleneck.

Should I forgo tagging previews? Would PIVOT result in the same amount of queries?

Answer 1

You can use a “join” to keep it all in one query. However: these kind of queries can get very “expensive”, escpecially if you are going to do some kind of grouping. So i would recommend to experiment with subselects. For example:

SELECT (
    SELECT GROUP_CONCAT(name)
    FROM   tags, posts_tags
    WHERE  posts_tags.posts_id = posts.posts_id
    AND    tags.tags_id = posts_tags.tags_id
) FROM posts LIMIT 10

With such kind of subselects you can normally get much better results than doing a normal join and grouping.

Caching is of course still a good idea …