Question

如何优化以下查询：

我有两张桌子，＆＃39; calendar_table＆＃39;和＆＃39;消费＆＃39;，我在这里用这个查询来计算每年的每月消费量。

日历表包含2005年至2009年的日，月和年，并且消费表已记录每月帐单周期的消费数据。此查询将计算每个帐单的天数，并使用该帐户查找每个月的消费量。

SELECT id,
        date_from as bill_start_date,
        theYear as Year,
        MONTHNAME(STR_TO_DATE(theMonth, '%m')) as month, 
        sum(DaysOnBill),
        TotalDaysInTheMonth,
        sum(perDayConsumption *  DaysOnBill) as EstimatedConsumption 
    FROM
    ( 
     SELECT
        id,
        date_from,
        theYear,
        theMonth,  # use theMonth for displaying the month as a number
        COUNT(*) AS DaysOnBill,
        TotalDaysInTheMonth, 
        perDayConsumption
    FROM
        (
        SELECT
            c.id,
            c.date_from as date_from,
            ct.dt,
            y AS theYear,
            month AS theMonth,
            DAY(LAST_DAY(ct.dt)) as TotalDaysInTheMonth,
            perDayConsumption
        FROM
            consumption AS c
            INNER JOIN
            calendar_table AS ct
                ON ct.dt >= c.date_from
                    AND ct.dt<= c.date_to
        ) AS allDates
    GROUP BY
        id,
        date_from,
        theYear,
        theMonth ) AS estimates
GROUP BY
        id,
        theYear,
        theMonth;

大约需要1000秒才能完成大约100万条记录。可以做些什么来加快速度吗？。

Answer 1

该查询有点可疑，假装首先进行一次分组，然后再与另一种分组，实际上并非如此。

首先，该法案一直在加入。然后我们按照账单加上月份和年份进行分组，从而获得月度数据视图。这可以在一次传递中完成，但查询首先加入，然后将结果用作聚合的派生表。最后再次采取结果，另一个＆＃34;另一个＆＃34;建立了一个组，它实际上与之前相同（账单加月和年）并且完成了一些伪聚合（例如sum（perDayConsumption * DaysOnBill），它与perDayConsumption * DaysOnBill相同，因为SUM仅在此处汇总一条记录）。

这可以写成：

SELECT
  c.id,
  c.date_from as bill_start_date,
  ct.y AS Year,
  MONTHNAME(STR_TO_DATE(ct.month, '%m')) as month,
  COUNT(*) AS DaysOnBill,
  DAY(LAST_DAY(ct.dt)) as TotalDaysInTheMonth,
  SUM(c.perDayConsumption) as EstimatedConsumption
FROM consumption AS c
INNER JOIN calendar_table AS ct ON ct.dt BETWEEN c.date_from AND c.date_to
GROUP BY
  c.id,
  ct.y,
  ct.month;

我不知道这是否会更快，或者MySQL的优化程序是否无法查看您的查询本身并将其归结为此无论如何。

如何优化下面使用三级select语句的查询？

1 个答案: