SQL Server查詢需要超過50秒才能執行

Question

我有一個查詢，我試圖運行。現在，我正在使用開始和結束日期參數。大約50秒後，我總共獲得了33排，我覺得這是非常多的時間。當我刪除參數時，返回1582行;這隻需要53秒即可返回。

我完全喪失了做什麼。我曾嘗試刪除任何多餘的連接（有幾個）;這沒有減少查詢返回時間。如果可能的話，能夠在30秒內返回查詢會很好。謝謝。

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，讓我們剔除期望與現實。這聽起來好像你邏輯上認爲Where語句會使你的查詢花費更少的時間。儘管邏輯上，這似乎是有道理的，但這不是SQL Server的運作方式。

考慮https://blog.sqlauthority.com/2009/04/06/sql-server-logical-query-processing-phases-order-of-statement-execution/from那裏我們看到的

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

SQL Server實際上你的WHERE參數完成完整的查詢然後限制它。如果非要在這個數據庫中的表管理訪問，我會考慮在加入索引，以最小：

• 現場Event_StartTime
• 事件ID，LinkedEventID和用戶名在每個表dwh.mcd_DWH_Events（如果不是主鍵）
• dwh.mcd_FWT_UserEventAssociations_Detailed_Manager現場Activity_TypeID現場Activity_MetaDataFieldValue

一個好的

views.mcd_FWT_ActivitiesExtraDetails經驗法則是日期和id應該被編入索引，並且一般而言，您將合理地定期將其放置到where語句中的任何字段。