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