where 1=-1 and 1=1 會不會影響查詢效率？
來源：程序員人生 發布時間：2015-08-20 08:37:45 閱讀次數：4493次
今天用sql profiler跟1個底層生成的SQL 的時候，跟到這樣1段代碼：
WITH TempQuery AS
(
SELECT *, ROW_NUMBER() OVER (ORDER BY CreateTime DESC) AS 'RowNumberForSplit'
FROM (select E.Name as Name, U.RealyName as RealyName,C.[Description] as Descriptions,'求職者' as tsf ,C.Result,C.CreateTime from [Mr].[User_Complaint] UC inner join [Mr].[User] U on UC.UserCode=U.Code inner join [Mr].[Complaint] C on UC.ComplaintCode=C.Code inner join [Mr].[Enterprise] E on UC.EnterpriseCode=E.Code union select E.Name as Name, U.RealyName as RealyName,C.[Description] as Descriptions,'企業' as tsf ,C.Result,C.CreateTime from [Mr].[Enterprise_Complaint] EC inner join [Mr].[Enterprise] E on EC.EnterpriseCode=E.Code inner join [Mr].[Complaint] C on EC.ComplaintCode =C.Code inner join [Mr].[User] U on EC.UserCode=U.Code) CP
WHERE 1 = 1 AND 1=1
)
SELECT *
FROM TempQuery
WHERE RowNumberForSplit BETWEEN 1 AND 10;
SELECT COUNT(1) AS TOTAL_COUNT FROM (select E.Name as Name, U.RealyName as RealyName,C.[Description] as Descriptions,'求職者' as tsf ,C.Result,C.CreateTime from [Mr].[User_Complaint] UC inner join [Mr].[User] U on UC.UserCode=U.Code inner join [Mr].[Complaint] C on UC.ComplaintCode=C.Code inner join [Mr].[Enterprise] E on UC.EnterpriseCode=E.Code union select E.Name as Name, U.RealyName as RealyName,C.[Description] as Descriptions,'企業' as tsf ,C.Result,C.CreateTime from [Mr].[Enterprise_Complaint] EC inner join [Mr].[Enterprise] E on EC.EnterpriseCode=E.Code inner join [Mr].[Complaint] C on EC.ComplaintCode =C.Code inner join [Mr].[User] U on EC.UserCode=U.Code) CP WHERE 1 = 1 AND 1=1
然后你就看到后面隨著的where 1=1 and 1=1,之前也用過這個東西拼過條件，但是后來有人說這樣影響查詢性能，再后來又有人說不影響。然后我就迷茫了。。。
還是自己做個實驗測試下吧。
首先，先看1下沒有這個條件的查詢：
/****** Script for SelectTopNRows command from SSMS ******/
SELECT TOP 100000 [RESOURCE_ID]
,[CLASS]
,[SORT_ID]
,[XML_CONTENT]
,[SEARCH_CONTENT]
,[ROW_ID]
FROM [MCS_WORKFLOW].[WF].[GENERIC_FORM_RELATIVE_DATA] WHERE 1=1 AND 1=1
然后使用履行計劃來估計下：
然后加入條件：
在履行計劃中可以看到，開消幾近全部在聚集索引表的掃描上，對照上圖，發現這兩張表數據1致。
嘿嘿，看來他們的查詢效力是1樣的。
but why????百度下吧。。。。
生活不易，碼農辛苦
如果您覺得本網站對您的學習有所幫助,可以手機掃描二維碼進行捐贈
