Mysql 分组数据求和

Question

我有以下表格:

产品(id、名称、价格、类别)

销售额(product_id，时间戳)

我必须对我的所有销售进行以下总结:

SELECT products.name AS products, TRUNCATE(products.price/100,2) as price, 
   COUNT(*) as sales_nbr, TRUNCATE(products.price/100*COUNT(*),2) as total
   FROM sales
   LEFT JOIN products ON sales.product_id=products.id
   GROUP BY product_id
   ORDER BY products.category

+-------------------+-------+-----------+--------+
| Products          | price | sales_nbr | total  |
+-------------------+-------+-----------+--------+
| Hot-dog           |  4.00 |    99     | 396.00 |
| Sandwich          |  4.00 |    64     | 256.00 |
| Croissant/brioche |  2.00 |    31     |  62.00 |
| Frites            |  5.00 |   106     | 530.00 |
...

我希望最后一行是这样的:

| TOTAL OF ALL SALES|       |   300     |1244.00 |
+-------------------+-------+-----------+--------+

我尝试使用 SUM() 和 UNION，但似乎没有任何效果:-)

Answer 1

你应该使用 ROLLUP which is explain here.

SELECT products.name AS products, TRUNCATE(products.price/100,2) as price, 
   COUNT(*) as sales_nbr, TRUNCATE(products.price/100*COUNT(*),2) as total
   FROM sales
   LEFT JOIN products ON sales.product_id=products.id
   GROUP BY product_id WITH ROLLUP
   ORDER BY products.category

或者，如果您只想对最后两列求和，您可以使用 union 来完成

SELECT products.name AS products, TRUNCATE(products.price/100,2) as price, 
   COUNT(*) as sales_nbr, TRUNCATE(products.price/100*COUNT(*),2) as total
   FROM sales
   LEFT JOIN products ON sales.product_id=products.id
   GROUP BY product_id 
UNION ALL
SELECT 'TOTAL OF ALL SALES' , null, 
   COUNT(*) as sales_nbr, SUM(TRUNCATE(products.price/100,2)) as total
   FROM sales
   LEFT JOIN products ON sales.product_id=products.id
ORDER BY products.category