def up
    sql = 'SELECT tag_id, user_id, created_at FROM following_tags'
    for tag in execute(sql)
      execute("INSERT INTO taggings (tag_id, taggable_id, taggable_type, context, created_at) VALUES(#{tag['tag_id']}, #{tag['user_id']}, 'User', 'following_tags', '#{tag['created_at']}')")
    end