text: CREATE TABLE tags (
    id SERIAL PRIMARY KEY,
    slug VARCHAR UNIQUE NOT NULL,
    tag_name VARCHAR UNIQUE NOT NULL
  );
  
  CREATE UNIQUE INDEX tags_slug_idx ON tags (slug);
  CREATE UNIQUE INDEX tags_name_idx ON tags (tag_name);
  
  CREATE TABLE photo_tags (
    id SERIAL PRIMARY KEY,
    photo_id INTEGER NOT NULL REFERENCES photos (id),
    tag_id INTEGER NOT NULL REFERENCES tags (id)
  );
  