添加一组SQL的总和

Question

sql新手，在查找查询示例时遇到困难。

所以，我有一张桌子：

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

我想找出哪种产品在某一个月卖得最好。2014年4月

让我们说：

| 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/在哪里为product_name使用GROUP BY。

Answer 1

您需要聚合，因为多个客户可以购买相同的产品。这反过来建议使用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
                               );

还有其他方式来表达这个查询。这似乎最接近你想要写的东西。

Answer 2

在没有进一步测试的情况下，应该是这样的：

SELECT product_name

FROM bought

WHERE month_bought = 'April' AND year_bought = 2014 AND 

       sum(quantity_buy) = (SELECT max(sum(quantity_buy)) FROM bought 

       WHERE month_bought = 'April' AND year_bought = 2014 group by  product_name)
group by product_name;

如果销售数量相同，这将返回多个产品。