元招聘 SQL -- 加入第 1 部分

Question

我已尽力将下面的元招聘问题排版得井井有条。我正在尝试确定该比率的当前查询是这样的。返回正确的 2/3 值，但比率返回全 1。对我出错的地方有帮助吗？

更新：在 David Aldridge

的帮助下

我意识到 SqlLite 是这里的问题，转换为数字有助于通过下面的解决方案中的查询获得最终结果。

背景：

以下模式是杂货店关系数据库的子集链。该连锁店向其销售许多不同产品类的产品不同商店的顾客。它还进行许多不同的促销活动。

我们要分析的四个表之间的关系如下图所示：

提示：

CMO 有兴趣了解销售量有何不同
产品系列受到促销活动的影响。
为此，对于每个可用的产品系列，
显示已售出的总单位数，
以及有效促销的已售单位比例
对于没有促销的售出单位， -- 按总销售量递增顺序排列。

解法：

SELECT product_family,
SUM(units_sold) as total_units_sold,
CAST(SUM(CASE WHEN s.promotion_id IS NOT 0 then units_sold * 1.0 ELSE 0 END) AS NUMERIC) / 
CAST(SUM(CASE WHEN s.promotion_id = 0 THEN units_sold * 1.0 ELSE 0 END) as NUMERIC) as ratio_units_sold_with_promo_to_sold_without_promo
FROM products p
JOIN product_classes c ON c.product_class_id = p.product_class_id
JOIN sales s ON s.product_id = p.product_id
GROUP BY product_family
ORDER BY total_units_sold ASC;

Answer 1

这感觉就像您要找的东西（为了清楚起见，我添加了一个额外的列）：

SELECT product_family,
      SUM(units_sold) as total_units_sold,
      SUM(CASE WHEN s.promotion_id > 0 then units_sold ELSE 0 END) as sold_when_promoted,
      SUM(CASE WHEN s.promotion_id > 0 then units_sold ELSE 0 END)::numeric /
        SUM(units_sold) AS ratio_units_sold_with_promo_to_sold_without_promo
FROM products p
JOIN product_classes c ON c.product_class_id = p.product_class_id
JOIN sales s ON s.product_id = p.product_id
GROUP BY product_family;

...或使用过滤子句...

SELECT product_family,
      SUM(units_sold) as total_units_sold,
      SUM(units_sold) filter(where s.promotion_id > 0) as sold_when_promoted,
      SUM(units_sold) filter(where s.promotion_id > 0)::numeric /
        SUM(units_sold) AS ratio_units_sold_with_promo_to_sold_without_promo
FROM products p
JOIN product_classes c ON c.product_class_id = p.product_class_id
JOIN sales s ON s.product_id = p.product_id
GROUP BY product_family;

我认为您不需要防止被零除，但如果您的某个产品的销售额总和为 zer，则您需要处理它。

编辑：我认为您实际上不需要参考促销 table。

Answer 2

SELECT product_family,
SUM(units_sold) as total_units_sold,
CAST(SUM(CASE WHEN s.promotion_id IS NOT 0 then units_sold * 1.0 ELSE 0 END) AS NUMERIC) / 
CAST(SUM(CASE WHEN s.promotion_id = 0 THEN units_sold * 1.0 ELSE 0 END) as NUMERIC) as ratio_units_sold_with_promo_to_sold_without_promo
FROM products p
JOIN product_classes c ON c.product_class_id = p.product_class_id
JOIN sales s ON s.product_id = p.product_id
GROUP BY product_family
ORDER BY total_units_sold ASC;

Answer 3

select   avg(case when is_low_fat_flg=1 and is_recyclable_flg=1 then 1 else 0 end)*100  as pct_low_fat_and_recyclable
from products

元招聘 SQL -- 加入第 1 部分

Meta Recruiting SQL -- Join Part 1

sql

sqlite

meta

提示：

解法：