gistfile1.sql

SELECT "drawings".* FROM "drawings"
  INNER JOIN "assignment_tag_drawings" ON ("drawings"."id" = "assignment_tag_drawings"."drawing_id")
  INNER JOIN "assignment_tags"         ON ("assignment_tags"."id" = "assignment_tag_drawings"."assignment_tag_id")
WHERE (drawings.assignment_id = 12
  AND assignment_tags.umbrella_category_id in ('29'))
GROUP BY drawings.id
  HAVING count(DISTINCT umbrella_category_id) = 1