SQL Server查询需要超过50秒才能执行

Question

我有一个查询，我试图运行。现在，我正在使用开始和结束日期参数。大约50秒后，我总共获得了33排，我觉得这是非常多的时间。当我删除参数时，返回1582行;这只需要53秒即可返回。

我完全丧失了做什么。我曾尝试删除任何多余的连接（有几个）;这没有减少查询返回时间。如果可能的话，能够在30秒内返回查询会很好。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，让我们剔除期望与现实。这听起来好像你逻辑上认为Where语句会使你的查询花费更少的时间。尽管逻辑上，这似乎是有道理的，但这不是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那里我们看到的

1. 操作的顺序
2. ON
3. OUTER
4. WHERE
5. GROUP BY
6. CUBE | ROLLUP
7. HAVING
8. 选择
9. DISTINCT 10 ORDER BY
10. TOP

SQL Server实际上你的WHERE参数完成完整的查询然后限制它。如果非要在这个数据库中的表管理访问，我会考虑在加入索引，以最小：

• 现场Event_StartTime
• 事件ID，LinkedEventID和用户名在每个表dwh.mcd_DWH_Events（如果不是主键）
• dwh.mcd_FWT_UserEventAssociations_Detailed_Manager现场Activity_TypeID现场Activity_MetaDataFieldValue

一个好的

views.mcd_FWT_ActivitiesExtraDetails经验法则是日期和id应该被编入索引，并且一般而言，您将合理地定期将其放置到where语句中的任何字段。