Select photos by multiple tags

Question

I have three MySQL tables - photos, tags and tagsphotos - and m:n relationship between photos and tags.

Photos:     id | filename | ...
Tags:       id | name
Tagsphotos: photo | tag

I want to select all photos with this condition:

(tagged as "dirty" AND tagged as "road") AND (tagged as "light.front" OR tagged as "light.side") AND (tagged as "perspective.two-point")

...which means that I want to find all pictures with dirty road, in two-point perspective and either with side or front light.

How can I do it? Thanks.

Answer 1

I think you're going to have to join the tags table to the photos table four times... pretty ugly.

SELECT Photos.*
FROM
  Photos
  JOIN (
    Tagsphotos JOIN Tags ON (Tags.id = Tagsphotos.tag)
  ) t1 ON (t1.photo = Photos.id)
  JOIN (
    Tagsphotos JOIN Tags ON (Tags.id = Tagsphotos.tag)
  ) t2 ON (t2.photo = Photos.id)
  JOIN (
    Tagsphotos JOIN Tags ON (Tags.id = Tagsphotos.tag)
  ) t3 ON (t3.photo = Photos.id)
  JOIN (
    Tagsphotos JOIN Tags ON (Tags.id = Tagsphotos.tag)
  ) t4 ON (t4.photo = Photos.id)
WHERE
      (t1.name = 'dirty' AND t2.name = 'road')
  AND (t3.name = 'light.front' OR t3.name = 'light.side')
  AND (t4.name = 'perspective.two-point')

Subqueries would probably be faster:

SELECT *
FROM Photos
WHERE
  Photos.id IN (
    SELECT Tagspohotos.photo
    FROM Tagsphotos JOIN Tags ON (Tags.id = Tagsphotos.tag)
    WHERE Tags.name = 'dirty'
  )
  AND Photos.id IN (
    SELECT Tagspohotos.photo
    FROM Tagsphotos JOIN Tags ON (Tags.id = Tagsphotos.tag)
    WHERE Tags.name = 'road'
  )
  AND Photos.id IN (
    SELECT Tagspohotos.photo
    FROM Tagsphotos JOIN Tags ON (Tags.id = Tagsphotos.tag)
    WHERE Tags.name = 'light.front' OR Tags.name = 'light.side'
  )
  AND Photos.id IN (
    SELECT Tagspohotos.photo
    FROM Tagsphotos JOIN Tags ON (Tags.id = Tagsphotos.tag)
    WHERE Tags.name = 'perspective.two-point'
  )