Question

I’m storing a simple tag relationship and I’m wondering what would be the better way to delete tags?

The two ways I know of:

1. SELECT tag FROM content_tags WHERE
   content_id = 10
2. Use php to compare the result with
   the new tags supplied and if there
   are any tags from the database
   result that are not in the new tags,
   run a delete query on that tag
3. The rest of the tags are either new
   or already exist so I use INSERT
   INTO content_tags … ON DUPLICATE
   KEY UPDATE

Or simply:

1. DELETE FROM content_tags FROM tags
   WHERE content_id = 10
2. Insert each tag (no need to use ON
   DUPLICATE KEY UPDATE here as the
   tags for this content_id are
   already deleted at this point)

I’m current doing the first method, but the 2nd way seems to be much less of a hassle. But I’m not sure if it’s “bad” or inefficient to use delete in this fashion. Or if you have a better method feel free to share.

Answer 1

You could adjust the first method to do also not do the inserts on tags that already exist. But it could (and probably will) still result in more queries then the second method, especially if you combine those insert statements in a single query.

//small example 🙂

INSERT INTO content_tags
(content_id, tag_id)
VALUES
(1,1),
(1,2),
(1,3);