如何修改此查询以添加一个新字段，其中包含原始记录总数的子集的某个字段的最大值？
[英]How can I modify this query to add a new field containing the maximum value of a field of a subset of the total original records?
问题描述
I am not so into database and I have the following problem implementing a query. 
我不太喜欢数据库，在实现查询时遇到以下问题。 I am using MySql 我正在使用MySql
I have a MeteoForecast table like this: 我有一个像这样的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;
It contains meteo forecast information, something like this: 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
So, as you can see in the previous dataset, each record have a starting datetime and and ending datetime. 因此，正如您在先前的数据集中看到的那样，每个记录都有一个开始日期时间和一个结束日期时间。 This because I am collecting more forecast information in a specific day (it is based on time range, in the example for each day a record from 06:00 am to 12:00 and another record from 12:00 to 18:00 pm). 这是因为我将在特定日期收集更多的预测信息（它基于时间范围，在示例中，每天的记录是从06:00 am到12:00，另一条记录是12:00到18:00 pm） 。
So, I created this simple query that extracts all the records in a specific range (in this case 2 days): 因此，我创建了一个简单的查询，该查询提取了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;
I have to modify this query in the following way: 我必须以以下方式修改此查询：
For each record retrieved by the previous query have to be added a new field named global_max_temp that is the maximum value of the max_temp field in the same day. 对于前一个查询检索到的每个记录，必须添加一个名为global_max_temp的新字段，该字段是同一天max_temp字段的最大值。
Doing an example related to the records related to theday having start_date value equal to 19/09/2017... , these are the records that I need to obtain: 做一个与与start_date值等于19/09/2017 ...的一天相关的记录相关的示例，这些是我需要获取的记录：
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
As you can see here the last field (inserted manually in this mock) is global_max_temp and in both records related to this day contains the value 22 because it is the maximum value of the max_temp field of all the records related to a specific day. 如您所见，最后一个字段（在此模拟中手动插入）是global_max_temp，并且与该天相关的两条记录中的值都为22，因为它是与特定日期相关的所有记录中max_temp字段的最大值。
This is the query calculating these global_max_temp value: 这是计算以下global_max_temp值的查询：
select max(max_temp) from MeteoForecast
where start_date = '2017-09-19 06:00:00'
How can I add this feature to my original query? 如何将此功能添加到原始查询中？
1 个解决方案
解决方案1
1 已采纳 2017-09-19 13:30:32
Can you try something like this: 你可以尝试这样的事情：
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;
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