难以在图表上显示大量值

Question

我正在尝试在图表上显示数据库中的一些记录。一分钟内保存的记录一般为70条左右。如此多的记录在折线图上看起来很疯狂，但当用户对数据感兴趣的时间间隔为四小时时，期望用户继续请求每分钟查看记录会更加疯狂和不现实。

我决定按分钟对记录进行分组，结果卡在了查询中。以下是我的查询示例：

SELECT DISNTINCT YEAR(recievedon), MONTH(recievedon), DAY(recievedon), HOUR(recievedon), referenceprice
FROM dbname
WHERE recievedon >= '2015-06-05 10:30' AND recievedon <= '2015-06-05 10:50'
ORDER BY recievedon

如何使用 GROUP BY 或 DISTINCT

按分钟对记录进行分组

其次，有没有更好的方法在（折线图）图表中呈现大型数据集而不是对记录进行分组？

Answer 1

如果我猜到你在使用 MySQL，那么你可以使用 to_seconds()。下面给出每分钟的平均参考价，以及区间内第一个价格的date/time：

select min(recievedon), avg(referenceprice)
from dbname
where recievedon >= '2015-06-05 10:30' AND recievedon <= '2015-06-05 10:50'
group by floor(to_seconds(receivedon) / 60)

编辑：

在SQL服务器中，您可以：

select min(receivedon), avg(referenceprice)
from dbname
where recievedon >= '2015-06-05 10:30' AND recievedon <= '2015-06-05 10:50'
group by datediff(minute, 0, receivedon);

如果您想要周期的开始而不是更早的时间戳：

select dateadd(minute, 0, datediff(minute, 0, receivedon)) as timeperiod,
       avg(referenceprice)
from dbname
where recievedon >= '2015-06-05 10:30' AND recievedon <= '2015-06-05 10:50'
group by dateadd(minute, 0, datediff(minute, 0, receivedon)) ;

Answer 2

使用简单的 group by DATEPART 而不用担心溢出。 SELECT 与 Gordon 的回答完全相同。

SELECT 
    MIN(ReceivedOn) AS Time,
    -- Assuming you need average price
    AVG(ReferencePrice) AS ReferencePrice
FROM
    dbname
WHERE
    ReceivedOn BETWEEN '2015-06-05 10:30' AND '2015-06-05 10:50'
GROUP BY
    DATEPART(YEAR, ReceivedOn),
    DATEPART(MONTH, ReceivedOn),
    DATEPART(DAY, ReceivedOn),
    DATEPART(HOUR, ReceivedOn),
    DATEPART(MINUTE, ReceivedOn)

难以在图表上显示大量值

Difficulty in displaying large number of values on a Chart

sql

sql-server

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