SQL Server查询需要50秒以上才能执行

Question

我有一个我正在尝试运行的查询。现在，我正在使用开始和结束日期参数。大约50秒后，我总共得到33行，我觉得这是一段非常多的时间。删除参数时，返回1582行;这只需要53秒才能返回。

我完全不知道该做什么。我试过取出任何冗余连接（有几个）;这没有减少查询返回时间。如果可能的话，能够在30秒内返回查询会很棒。谢谢。

DECLARE @StartDate DATETIME
SET @StartDate = '2017-04-30 00:00:00.000'
SET @EndDate = '2017-07-31 08:00:00.000'
SELECT
 a.PrimaryEventID, 
 b.Event_Name as 'PrimaryEventName',
 b.Event_StartTime as 'EventDate',
 e.UserLastName+', '+e.UserFirstName as 'Operator',
 f.Activity_MetaDataFieldValue as 'Type',
 'Status' = Case
        When c.EventStatus = 0 then 'Tent' 
        When c.EventStatus = 1 then 'Appr' 
        When c.EventStatus = 2 then 'Pend' 
        Else 'No Status Found' 
 End,
 CONVERT(varchar(20), a.PrimaryEventID)+'|'+CONVERT(varchar(20), e.UserId) 
 as 'JoinColumn',
 b1.Activity_MetaDataTypeID
FROM
  views.mcd_DWH_LinkedEvents a
  Left JOIN dwh.mcd_DWH_Events b ON a.PrimaryEventID = b.Event_ID
  Left JOIN rawViews.mcd_DWH_ActivitiesBasicData b1 on b.EventActivity_ID = b1.Activity_ID
  Left JOIN dwh.mcd_DWH_Events c ON a.LinkedEventID = c.Event_ID
  Left JOIN dwh.mcd_FWT_UserEventAssociations_Detailed_Manager d ON a.LinkedEventID = d.Event_ID 
  Left JOIN views.mcd_FWT_UsersBasicData e ON d.User_ID = e.UserID
  Left JOIN views.mcd_FWT_ActivitiesExtraDetails f ON c.EventActivity_ID = f.Activity_ID and f.Activity_MetaDataFieldName = 'Type'
  Left JOIN views.mcd_FWT_TrainingProgramsBasicData g ON c.EventTrainingProgram_ID = g.TrainingProgramID
  Left JOIN views.mcd_FWT_MPlansBasicData h ON g.TrainingProgram_MPlanID = h.MPlanID
WHERE d.Activity_TypeID = 57 
  and b.Event_StartTime between @StartDate and @EndDate
  and (f.Activity_MetaDataFieldValue = 'Qual' or f.Activity_MetaDataFieldValue = 'Run' or f.Activity_MetaDataFieldValue = 'Assess' ) 
GROUP by a.PrimaryEventID, b.Event_Name,b.Event_StartTime, h.MPlanName, f.Activity_MetaDataFieldValue, e.UserLastName, e.UserFirstName, c.EventStatus, e.UserId, b1.Activity_MetaDataTypeID

Answer 1

首先，让我们扼杀期望与现实。听起来好像你逻辑上假设Where语句会让你的查询花费更少的时间。从逻辑上讲，这似乎是有道理的，这不是SQL Server的运作方式。

考虑https://blog.sqlauthority.com/2009/04/06/sql-server-logical-query-processing-phases-order-of-statement-execution/from，我们看到了

的操作顺序

1. FROM
2. ON
3. OUTER
4. WHERE
5. GROUP BY
6. CUBE | ROLLUP
7. HAVING
8. 选择
9. DISTINCT 10订购
10. TOP

SQL Server实际上完成了完整查询然后通过WHERE参数限制它。如果您对此数据库中的表具有管理访问权限，我会考虑至少添加索引：

• dwh.mcd_DWH_Events on field Event_StartTime
• 每个表中的EventID，LinkedEventID和UserID（如果不是主键）
字段Activity_TypeID上的
• dwh.mcd_FWT_UserEventAssociations_Detailed_Manager
• views.mcd_FWT_ActivitiesExtraDetails on field Activity_MetaDataFieldValue

一个好的经验法则是日期和ID应该被编入索引，一般来说，你可以合理地定位到where语句中的任何字段。