基于条件多列标准的最佳过滤

Question

我需要根据条件条件过滤查询。看起来很简单，我只是在寻找优化查询的想法

我需要根据季节、国家和产品过滤价格。所以查询或多或少会像：

    SELECT Country, Season, Product, Price
FROM Table
WHERE (Country = 'UK' AND Season = 'High' AND Product = 'X' AND Price < 30)
OR
(Country = 'ES' AND Season = 'Low' AND Product = 'Y' AND Price < 25)
OR 
(Country = 'FR' AND Season = 'Mid' AND Product = 'Z' AND Price < 50)

等等。问题是组合的数量是巨大的，这将使这不切实际。欢迎任何想法

Answer 1

假设您所有的ANDed 表达式都有相同的列，那么大多数数据库都会很好地处理您的查询。他们会在 (Country, Season, Product, Price).

上使用索引

如果你有这样的索引并且没有重叠的条件，你也可以将逻辑表述为：

SELECT Country, Season, Product, Price
FROM Table
WHERE Country = 'UK' AND Season = 'High' AND Product = 'X' AND Price < 30
UNION ALL
SELECT Country, Season, Product, Price
FROM Table
WHERE Country = 'ES' AND Season = 'Low' AND Product = 'Y' AND Price < 25
UNION ALL
. . .

这更灵活。如果不是所有条件都完全相同，这仍然可以使用索引进行查询。

您也可以使用JOIN 来表达这一点。在查询中，您可以创建派生表：

SELECT Country, Season, Product, Price
FROM (VALUES ('UK', 'High', 'X', 20),
             ('ES', 'LOW', 'Y', 25),
             . . . 
     ) v(Country, Season, Product, Price) JOIN
     Table t
     ON t.country = v.country AND
        t.season = v.season AND
        t.product = v.product AND
        t.price < v.price;

您希望该查询使用相同（或相似）的索引。

当然，您可以将值存储在单独的表中。