Question

现在已经工作了几个小时，我想知道在SQL中是否有推荐的解决方案，或者我最好把它放在我的应用程序逻辑而不是数据库中。我更喜欢前者。

CREATE TABLE `rate_info` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`city` varchar(100) DEFAULT NULL,
`rate_type` varchar(45) DEFAULT NULL,
`rate` int(11) DEFAULT NULL,
`vendor` varchar(45) DEFAULT NULL,
`product` varchar(45) DEFAULT NULL,
`days_to_pickup` int(11) DEFAULT NULL,
`timestamp` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
`state` varchar(45) DEFAULT NULL,
`country` varchar(45) DEFAULT NULL,
 PRIMARY KEY (`id`)
 ) ENGINE=InnoDB AUTO_INCREMENT=787 DEFAULT CHARSET=latin1$$

鉴于城市，州和城市，我需要对每种产品和供应商组合的平均费率进行最佳估算。国家。每个供应商可以拥有不同数量的产品。此外，每个城市的供应商数量可能不同。逻辑需要

如果找到匹配项，则返回与城市，州和国家/地区匹配的记录的数据。
如果找不到匹配项，请尝试根据州和州找到结果。国家。
如果这也没有返回任何内容，请仅根据国家/地区查找结果
最后，使用所有记录来计算每种产品，供应商组合的平均费率
其他列还有其他逻辑，但它们都遵循与位置相同的模式。

第一个查询将类似于

select avg(rate) rate, vendor, product from rate_info
where city = 'Boston'
and state = 'MA'
and country = 'United States'
and rate_type = 'REGULAR'
and days_to_pickup >= 4
group by vendor, product

我一直在玩COALESCE，CASE，IFNULL，但无法让查询工作。我可以在应用程序层中执行此操作，但是我必须对数据库进行多次调用，因为很可能不会遇到第一种情况。

理想的解决方案就像是

COALESCE(select_city_state_cntr, select_state_cntry, select_cntry);

如果遗漏了某些内容，请告诉我，我会根据需要添加更多详细信息。

谢谢

Answer 1

这是一个可能的解决方案。查询所有三种方式，并使用LIMIT取第一个匹配的方式。

SELECT * FROM (
 (SELECT SUM(population) AS population, city, state, country
  FROM POPULATION
  WHERE (city, state, country) = (?, ?, ?))
 UNION ALL
 (SELECT SUM(population), NULL, state, country
  FROM POPULATION
  WHERE (state, country) = (?, ?))
 UNION ALL
 (SELECT SUM(population), NULL, NULL, country
  FROM POPULATION
  WHERE (country) = (?))) AS t
WHERE t.population IS NOT NULL
LIMIT 1;

Answer 2

一种方法是：

CREATE TABLE `population` (
  `city` varchar(64) NOT NULL,
  `state` varchar(64) NOT NULL,
  `country` varchar(64) NOT NULL,
  `population` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

和一个选择查询：

SELECT city, state, country, population
  FROM population
 WHERE country = '<country>' AND state = '<state>' AND city = '<city>'
UNION
SELECT null, state, country, sum(population)
  FROM population
 WHERE country = '<country>' AND state = '<state>'
 GROUP BY state
UNION
SELECT null, null, country, sum(population)
  FROM population
 WHERE country = '<country>'
 LIMIT 1;

Answer 3

这应该给你正确的结果（如果我的要求是正确的），虽然它没有效率，因为它计算所有选项，即使在找到exect城市的情况下：

SELECT 
  (city = 'Boston') * rate AS exactCityData, 
  SUM((city != 'Boston' AND state = 'MA') * rate) AS wholeStateData, 
  SUM((city != 'Boston' AND state != 'MA' AND country = 'United States') * rate) AS wholeCountryData
WHERE country = 'United States'
GROUP BY vendor, product;

对于州平均值，您不能使用AVG，因为查询匹配所有行（在国家/地区），因此查询应该是这样的：

SELECT 
  (city = 'Boston') * rate AS exactCityData, 
  SUM((state = 'MA') * rate) / SUM(state = 'MA') AS wholeStateData, 
  AVG(rate) AS wholeCountryData
WHERE country = 'United States'
GROUP BY vendor, product;

现在用于“最后的手段”选项，删除国家/地区要求，并将AVG(rate) AS wholeCountryData部分替换为SUM((country = 'United States') * rate) / SUM(country = 'United States') AS wholeCountryData

MYSQL-控制流功能

3 个答案: