Question

I have a MySQL database with 3 tables:

1. The main table of records called
   “tracks” (as in music)
2. A tags table
   called “tags”
3. A join table for the two called “taggings”

The tags table is basically a list of genres, which is pre-defined. A track can then have 1 or more tags (via the join table).

The idea is, that the user checks off the genres (tags) for which he or she want to find tracks. But I would also like the interface to reflect which tags are no longer “useful”, that is, tags which are complementary to the currently selected ones.

Edit: What I missed was that I need to find tags that are complementary to the currently selected set of tags. See my comment below.

Example: the user selects the “rock” and “pop” tags, and is shown a list of tracks that match “rock” + “pop”. But suppose there are no tracks in the database that also match “jazz”. In that case, I’d like to disable the “jazz” tag in the interface, because “rock” + “pop” + “jazz” would give zero results.

Is there a clever way to do this with MySQL?

Answer 1

Ended up doing this:

• When a track is tagged, its tag IDs are concatenated (in order) and added to a 1-column lookup table (and of course also to taggings). E.g. “,1,2,4,6,9,” is added to the lookup (there’s a reason for the leading/trailing commas)
• When tags are selected while searching, they’re similarly concatenated, and used in a LIKE clause which selects all the concatenations from the lookup table that contain those tag IDs
• The found concatenations are then processed to get all the IDs that they contain
• Whichever IDs are not in the resulting list are thus complementary to the selected ones