重新排序汇总的输出，其中小计显示在相应类别的开头或结尾

如何解决重新排序汇总的输出，其中小计显示在相应类别的开头或结尾

我们希望汇总中的小计显示在每个相应类别的开头/结尾。以下是我们尝试过的对下表的查询。但是，Coalesce 不会用“total”替换空值，因为输出中没有显示空值或“total”，这意味着汇总不起作用。我们的假设是，某些东西与脚本的序列（与序列）不符。我们只熟悉Postgres sql。感谢您的任何建议！

表格

客户表：

|  customer_id|customer_name|segment    |
  -----------  -----------   ----------
|1            |Bob          |Consumer   |
|2            |Mary         |Corporate  |
|3            |Bill         |Home Office|
|4            |Kathy        |Consumer   |

产品表：

|product_id      |category  |sub_category|product_name            |
 --------------  ----------  -----------  -----------------------
|FUR-ADV-10000002|furniture |furnishings |Advantus Clock Ergonomic|
|FUR-BO-10000002 |furniture |bookcases   |Bush Classic Bookcase   |
|TEC-bro-10000348|technology|copiers     |brother copy Machine    |
|TEC-EPS-10000053|technology|machines    |Epson Printer Red       |
|OFF-AR-10000019 |office sup|art         |BIC Highlighters Blue   |
|OFF-EAT-10000522|office sup|paper       |Eaton Comp Printout     |

订单表：

|order_id       |product_id      |customer_id|sales |
 --------------  ---------------  ----------  -----
|AE-2016-1308551|FUR-ADV-10000002|1          |82.67 |
|AE-2016-1308552|FUR-BO-10000002 |1          |101.54|
|AE-2016-1308553|TEC-bro-10000348|2          |79.28 |
|AE-2016-1308554|TEC-EPS-10000053|3          |101.23|
|AE-2016-1308555|OFF-AR-10000019 |4          |39.78 |

查询：

SELECT COALESCE(products.category,'total'),COALESCE(products.sub_category,SUM(orders.sales) AS total_sales
FROM products
        INNER JOIN orders
        ON products.product_id=orders.product_id,(SELECT products.category,products.sub_category,SUM (orders.sales)
        FROM orders
        INNER JOIN products
        ON orders.product_id=products.product_id
        GROUP BY
            ROLLUP (1,2)) t
        GROUP BY 1,2
        ORDER BY 3 desc;