[英]SELECT set of most recent id, amount FROM table, where id occurs many times
I have a table recording the amount of data transferred by a given service on a given date. 我有一张表,记录着给定服务在给定日期传输的数据量。 One record is entered daily for a given service.
每天为给定服务输入一条记录。
I'd like to be able to retrieve the most recent amount
for a set of services. 我希望能够检索一组服务的最新
amount
。
Example data set: 数据集示例:
serviceId | amount | date
-------------------------------
1 | 8 | 2010-04-12
2 | 11 | 2010-04-12
2 | 14 | 2010-04-11
3 | 9 | 2010-04-11
1 | 6 | 2010-04-10
2 | 5 | 2010-04-10
3 | 22 | 2010-04-10
4 | 17 | 2010-04-19
Desired response (service ids 1,2,3): 所需的响应(服务ID 1,2,3):
serviceId | amount | date
-------------------------------
1 | 8 | 2010-04-12
2 | 11 | 2010-04-12
3 | 9 | 2010-04-11
Desired response (service ids 2, 4): 所需的响应(服务ID 2、4):
serviceId | amount | date
-------------------------------
2 | 11 | 2010-04-12
4 | 17 | 2010-04-19
This retrieves the equivalent as running the following once per serviceId: 这将检索等效结果,即每个serviceId运行一次以下命令:
SELECT serviceId, amount, date
FROM table
WHERE serviceId = <given serviceId>
ORDER BY date DESC
LIMIT 0,1
I understand how I can retrieve the data I want in X queries. 我了解如何在X查询中检索所需的数据。 I'm interested to see how I can retrieve the same data using either a single query or at the very least less than X queries.
我很想知道如何使用单个查询或至少少于X个查询来检索相同的数据。
I'm very interested to see what might be the most efficient approach. 我非常想知道什么是最有效的方法。 The table currently contains 28809 records.
该表当前包含28809条记录。
I appreciate that there are other questions that cover selecting the most recent set of records. 我很欣赏还有其他问题涉及选择最新记录集。 I have examined three such questions but have been unable to apply the solutions to my problem.
我已经检查了三个这样的问题,但是无法将解决方案应用于我的问题。
select m.*
from (
select serviceId, max(date) as MaxDate
from MyTable
group by serviceId
) mm
inner join MyTable m on mm.serviceId = m.serviceId and mm.MaxDate = m.date
If you wish to filter by serviceId, you can do: 如果希望按serviceId进行过滤,则可以执行以下操作:
select m.*
from (
select serviceId, max(date) as MaxDate
from MyTable
where serviceId in (1, 2, 3)
group by serviceId
) mm
inner join MyTable m on mm.serviceId = m.serviceId and mm.MaxDate = m.date
SELECT serviceId, amount, date
FROM table as t
WHERE NOT EXIST (
SELECT * FROM table as x
WHERE t.serviceId = x.serviceID AND t.date < x.date
)
if you want to filter out some serviceIds than 如果您想过滤掉一些serviceIds
SELECT serviceId, amount, date
FROM table as t
WHERE NOT EXIST (
SELECT * FROM table as x
WHERE t.serviceId = x.serviceID AND t.date < x.date
)
AND serviceId in (2, 4)
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