Question

SQL：

select distinct DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0) as Date,
(select count(*) from Raw_Mats A where DateAdd(Day, DateDiff(Day, 0, A.Receive_date), 0)=DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0)) as Total,
(select count(*) from Raw_Mats B where DateAdd(Day, DateDiff(Day, 0, B.Receive_date), 0)=DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0) and B.status='Solved') as Delivered,
(select count(*) from Raw_Mats C where DateAdd(Day, DateDiff(Day, 0, C.Receive_date), 0)=DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0) and C.status='Pending') as UnDelivered
from Raw_Mats m where m.Receive_date between '2011-07-01' and '2011-07-21'

如何提高上述查询的性能。这需要44秒。想要不到10秒

由于

Answer 1

您有Receive_date和status的索引吗？（不是每个的索引，合并）

此外：

表中有4个触摸，这意味着查询将至少缩放为O（4n）。通过使用COUNT（CASE），您可以删除Delivered和UnDelivered子查询
您需要GROUP BY。你的DISTINCT是一个解决这个问题的工作
BETWEEN为>=和<=，这对于有时间的日期通常不正确

为了清楚起见，我在这里使用了一个子查询，但这并不重要：

select
   DateOnly as Date,
   COUNT(*) AS Total,
   COUNT(CASE WHEN status='Solved' THEN 1 END) AS Delivered,
   COUNT(CASE WHEN status='Pending' THEN 1 END) AS UnDelivered
from
   (
   SELECT
       DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0) as DateOnly,
       status
   FROM
      Raw_Mats
   WHERE
      Receive_date >= '2011-07-01' AND Receive_date < '2011-07-21'
   ) T
 GROUP BY
   DateOnly

编辑，没有子查询。

我从一个子查询开始，因为我认为它比预期更复杂，并且不打算把它拿出来......

select
   DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0) as Date,
   COUNT(*) AS Total,
   COUNT(CASE WHEN status='Solved' THEN 1 END) AS Delivered,
   COUNT(CASE WHEN status='Pending' THEN 1 END) AS UnDelivered
from
   Raw_Mats
WHERE
   Receive_date >= '2011-07-01' AND Receive_date < '2011-07-21'
GROUP BY
   DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0)

Answer 2

分而治之：只需将sql的每个部分作为单独的语句进行尝试，您就会发现哪个部分很慢。如果您有子选择和函数，那么服务器很可能需要临时表来执行选择，如果您没有足够的内存（或大型数据集或配置您的SQL服务器来执行此操作），临时对象被交换到磁盘，这也使它变慢。

Answer 3

查询太多子查！摆脱其中的一些，它会有所帮助。此外，您不应在sqls中使用双方的功能。

例如：

where DateAdd(Day, DateDiff(Day, 0, A.Receive_date), 0)=
              DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0)

在这种特定情况下，db引擎必须遍历所有行以评估DateDiff(Day, 0, A.Receive_date) and DateAdd(Day, DateDiff(Day, 0, A.Receive_date), 0)，然后将其与右侧进行比较，这也是一个函数！这简直就是一场灾难。

另外，你有Receive_date的索引吗？如果没有添加它。

增加SQL查询性能

3 个答案: