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如何修改此查询以添加一个新字段,该字段包含总原始记录子集的字段的最大值?

rdbms database sql mysql

AndreaNobili · 技术社区 · 7 年前

我有这样一个MeteoForecast表:

CREATE TABLE MeteoForecast (
  id                   BigInt(20) NOT NULL AUTO_INCREMENT,
  localization_id      BigInt(20) NOT NULL,
  seasonal_forecast_id BigInt(20),
  meteo_warning_id     BigInt(20),
  start_date           DateTime NOT NULL,
  end_date             DateTime NOT NULL,
  min_temp             Float,
  max_temp             Float,
  icon_link            VarChar(255) CHARACTER SET latin1 COLLATE latin1_swedish_ci NOT NULL, 
  PRIMARY KEY (
      id
  )
) ENGINE=InnoDB AUTO_INCREMENT=3 ROW_FORMAT=DYNAMIC DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci;

它包含气象预报信息,如下所示:

id                   localization_id      start_date              end_date                min_temp             max_temp             icon_link                                                                                                                                                                                                                                                      
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1                    1                    18/09/2017 06:00:00     18/09/2017 12:00:00     15                   24                   Mostly_Cloudy_Icon.png                                                                                                                                                                                                                                         
2                    1                    18/09/2017 12:00:00     18/09/2017 18:00:00     15                   24                   Light_Rain.png                                                                                                                                                                                                                                                 
3                    1                    19/09/2017 06:00:00     19/09/2017 12:00:00     12                   22                   Mostly_Cloudy_Icon.png                                                                                                                                                                                                                                         
4                    1                    19/09/2017 12:00:00     19/09/2017 18:00:00     13                   16                   Mostly_Cloudy_Icon.png                                                                                                                                                                                                                                         
5                    1                    20/09/2017 06:00:00     20/09/2017 12:00:00     18                   26                   Light_Rain.png                                                                                                                                                                                                                                                 
6                    1                    20/09/2017 12:00:00     20/09/2017 18:00:00     17                   25                   Light_Rain.png

因此,我创建了一个简单的查询,用于提取特定范围内的所有记录(在本例中为2天):

select * from MeteoForecast 
where start_date between  '2017-09-18 06:00:00' and '2017-09-20 06:00:00'
order by start_date desc;

我必须按以下方式修改此查询:

对于上一个查询检索到的每个记录,必须添加一个名为 全局最大温度 这是 最高温度

做一个与日期相关的记录相关的示例 开始日期 ,以下是我需要获得的记录:

id                   localization_id      start_date              end_date                min_temp             max_temp             icon_link                       global_max_temp                                                                                                                                                                                                                                                      
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------    
3                    1                    19/09/2017 06:00:00     19/09/2017 12:00:00     12                   22                   Mostly_Cloudy_Icon.png          22                                                                                                                                                                                                                                     
4                    1                    19/09/2017 12:00:00     19/09/2017 18:00:00     13                   16                   Mostly_Cloudy_Icon.png          22

如您所见,最后一个字段(在此模拟中手动插入)是在与这一天相关的两个记录中都包含了价值因为它是 最高温度 与特定日期相关的所有记录的字段。

这是计算这些的查询 全局最大温度 价值:

select max(max_temp) from MeteoForecast 
where start_date = '2017-09-19 06:00:00'

如何将此功能添加到原始查询?

1 回复 | 直到 7 年前

etsa 7 年前

你能试试这样的东西吗

SELECT A.*, B.GLOBAL_MAX_TEMP
FROM (
    select id, start_date, end_date, min_temp, max_temp
    from MeteoForecast 
    where start_date between  '2017-09-18 06:00:00' and '2017-09-20 06:00:00'
    ) A
INNER JOIN (SELECT  date(start_date) AS date_only, MAX(max_temp) AS GLOBAL_MAX_TEMP
            FROM MeteoForecast
            WHERE start_date BETWEEN  '2017-09-18 06:00:00' and '2017-09-20 06:00:00'
            GROUP BY date(start_date)
            ) B ON date(A.start_date) = B.date_only
ORDER by start_date desc;