WITH all_sales AS (
  SELECT
    d_year,
    i_brand_id,
    i_class_id,
    i_category_id,
    i_manufact_id,
    SUM(sales_cnt) AS sales_cnt,
    SUM(sales_amt) AS sales_amt
  FROM (
         SELECT
           d_year,
           i_brand_id,
           i_class_id,
           i_category_id,
           i_manufact_id,
           cs_quantity - COALESCE(cr_return_quantity, 0) AS sales_cnt,
           cs_ext_sales_price - COALESCE(cr_return_amount, 0.0) AS sales_amt
         FROM catalog_sales
           JOIN item ON i_item_sk = cs_item_sk
           JOIN date_dim ON d_date_sk = cs_sold_date_sk
           LEFT JOIN catalog_returns ON (cs_order_number = cr_order_number
             AND cs_item_sk = cr_item_sk)
         WHERE i_category = 'Books'
         UNION
         SELECT
           d_year,
           i_brand_id,
           i_class_id,
           i_category_id,
           i_manufact_id,
           ss_quantity - COALESCE(sr_return_quantity, 0) AS sales_cnt,
           ss_ext_sales_price - COALESCE(sr_return_amt, 0.0) AS sales_amt
         FROM store_sales
           JOIN item ON i_item_sk = ss_item_sk
           JOIN date_dim ON d_date_sk = ss_sold_date_sk
           LEFT JOIN store_returns ON (ss_ticket_number = sr_ticket_number
             AND ss_item_sk = sr_item_sk)
         WHERE i_category = 'Books'
         UNION
         SELECT
           d_year,
           i_brand_id,
           i_class_id,
           i_category_id,
           i_manufact_id,
           ws_quantity - COALESCE(wr_return_quantity, 0) AS sales_cnt,
           ws_ext_sales_price - COALESCE(wr_return_amt, 0.0) AS sales_amt
         FROM web_sales
           JOIN item ON i_item_sk = ws_item_sk
           JOIN date_dim ON d_date_sk = ws_sold_date_sk
           LEFT JOIN web_returns ON (ws_order_number = wr_order_number
             AND ws_item_sk = wr_item_sk)
         WHERE i_category = 'Books') sales_detail
  GROUP BY d_year, i_brand_id, i_class_id, i_category_id, i_manufact_id)
SELECT
  prev_yr.d_year AS prev_year,
  curr_yr.d_year AS year,
  curr_yr.i_brand_id,
  curr_yr.i_class_id,
  curr_yr.i_category_id,
  curr_yr.i_manufact_id,
  prev_yr.sales_cnt AS prev_yr_cnt,
  curr_yr.sales_cnt AS curr_yr_cnt,
  curr_yr.sales_cnt - prev_yr.sales_cnt AS sales_cnt_diff,
  curr_yr.sales_amt - prev_yr.sales_amt AS sales_amt_diff
FROM all_sales curr_yr, all_sales prev_yr
WHERE curr_yr.i_brand_id = prev_yr.i_brand_id
  AND curr_yr.i_class_id = prev_yr.i_class_id
  AND curr_yr.i_category_id = prev_yr.i_category_id
  AND curr_yr.i_manufact_id = prev_yr.i_manufact_id
  AND curr_yr.d_year = 2002
  AND prev_yr.d_year = 2002 - 1
  AND CAST(curr_yr.sales_cnt AS DECIMAL(17, 2)) / CAST(prev_yr.sales_cnt AS DECIMAL(17, 2)) < 0.9
ORDER BY sales_cnt_diff
LIMIT 100