mysql - 添加一组 SQL 的总和

Question

刚接触 SQL，无法找到查询示例。

所以，我有一张 table :

bought ( customer_name, month, year, quantity, product_name )

我想找到特定月份 EX 中销量最高的产品。 2014 年 4 月

可以说:

| Jan | April | 2014 | 7 | Watches |
| Ron | April | 2014 | 4 |  Rings  |
| Jan | April | 2014 | 4 |  Rings  |

现在我有:

SELECT product_name
FROM bought
WHERE month_bought = 'April' AND year_bought = 2014 AND 
           quantity_buy >= all (SELECT quantity_buy
                                FROM bought 
                                WHERE month_bought = 'April' AND year_bought = 2014
                               );

我不确定是否/在哪里使用 GROUP BY 作为产品名称。

Answer 1

您需要聚合，因为多个客户可能购买相同的产品。这反过来又建议使用 HAVING 而不是 WHERE:

SELECT product_name
FROM bought b
WHERE month_bought = 'April' AND year_bought = 2014 
GROUP BY product_name
HAVING SUM(quantity_buy) >= all (SELECT SUM(b2.quantity_buy)
                                 FROM bought b2
                                 WHERE b2.month_bought = b.month_bought AND 
                                       b2.year_bought = b.year_bought
                                 GROUP BY product_name
                               );

还有其他方法可以表达此查询。这似乎最接近您要写的内容。