Question

Consider following tables structure:

users (user_id, ...)
images (image_id, user_id, ...)
tag_links (tag_id, image_id)
tags_names (tag_id, tag_name)

Let’s say any given user_id has multiple images in the images table, and an image has multiple tags stored in tag_links.

How can I join these tables in order to get all tag_names used by any given user_id on all of his images? Are these kind of queries (joing multiple tables) slow and not recommended, or is it common to do that?

Answer 1

Joining is common and it’s the way it should be done.

SELECT tn.tag_name
FROM tags_names AS tn
INNER JOIN tag_links AS tl ON tn.tag_id=tl.tag_id
INNER JOIN images AS i ON tl.image_id=i.image_id
WHERE i.user_id=YOURUSERID

Your table design though only makes sense if a tag can have more then one name, if not use a column name on tag_links.