Question

I have 3 tables (scenes, categories, scenes_categories ) in a many to many relationship.

scenes ( id, title, description )
categories ( id, title )
scenes_categories ( scene_id, category_id )

I’m having problems making a query to select scenes that must match multiple categories. For example, I might want to select scenes that match category 3 AND category 5 AND category 8, but I can’t figure out how to get this to work.

So far I’ve got something like

SELECT scenes.id, scenes.title, scenes.description
FROM scenes
LEFT JOIN scenes_categories ON scenes.id = scenes_categories.scene_id
LEFT JOIN categories ON scenes_categories.category_id = categories.id
WHERE scenes_categories.category_id = '3'
AND scenes_categories.category_id = '5'
AND scenes_categories.category_id = '8'
AND scenes.id = '1'

How can I select for records that must match all the category ID’s specified?

Answer 1

You need to require that a row exists in your many-to-many table for that sceneId, for each categoryId you are requiring:
So try this:

SELECT s.id, s.title, s.description
FROM scenes s
WHERE s.id = '1'
   And Exists (Select * From scenes_categories 
               Where scene_id = s.Id
                  And category_id = '3')
   And Exists (Select * From scenes_categories 
               Where scene_id = s.Id
                  And category_id = '5')

   And Exists (Select * From scenes_categories 
               Where scene_id = s.Id
                  And category_id = '8')

another option that should work is to do three inner joins instead:

SELECT s.id, s.title, s.description
FROM scenes s
  Join scenes_categories c3 
      On c3.scene_id  = s.Id
           And c3.category_id ='3'
  Join scenes_categories c5 
      On c5.scene_id  = s.Id
           And c5.category_id ='5'
  Join scenes_categories c8 
      On c8.scene_id  = s.Id
           And c8.category_id ='8'     
WHERE s.id = '1'