实体框架生成不同的sql查询

Question

i have below code for getting one field from a table

var a = db.Customs
          .Where(x => x.Cust_ID == tid)
          .Select(x => x.TransferCommission.Value)
          .FirstOrDefault().ToString();

and this code generates below SQL query

SELECT TOP (1) 
[Extent1].[TransferCommission] AS [TransferCommission]
FROM [dbo].[Custom] AS [Extent1]
WHERE 54612 = [Extent1].[Cust_ID]

but this code

var b = db.Tours
          .Where(x => x.Tour_ID == tid)
          .Select(x => x.Supl_ID.Value)
          .FirstOrDefault()
          .ToString();

generates below SQL query

exec sp_executesql N'SELECT 
[Limit1].[Supl_ID] AS [Supl_ID]
FROM ( SELECT TOP (1) 
    [Extent1].[Supl_ID] AS [Supl_ID]
    FROM (SELECT 
[Toursn].[Airline_ID] AS [Airline_ID], 
[Toursn].[Tour_Code] AS [Tour_Code], 
[Toursn].[Supl_ID] AS [Supl_ID], 
[Toursn].[Start_Destination_ID] AS [Start_Destination_ID], 
[Toursn].[End_Destination_ID] AS [End_Destination_ID], 
[Toursn].[Tour_Name] AS [Tour_Name], 
[Toursn].[Service_Category_ID] AS [Service_Category_ID], 
[Toursn].[Tour_Option_Name] AS [Tour_Option_Name], 
[Toursn].[Run_MinPax] AS [Run_MinPax], 
[Toursn].[Notes] AS [Notes], 
[Toursn].[Advse_Book] AS [Advse_Book], 
[Toursn].[Tour_Desc] AS [Tour_Desc], 
[Toursn].[Tour_Duration] AS [Tour_Duration], 
[Toursn].[Distance] AS [Distance], 
[Toursn].[Tour_ID] AS [Tour_ID], 
[Toursn].[Tour_Map1] AS [Tour_Map1], 
[Toursn].[Tour_Num_Days_Cruise] AS [Tour_Num_Days_Cruise], 
[Toursn].[Tour_Itinerary_File] AS [Tour_Itinerary_File], 
[Toursn].[Cruise_Supl_ID] AS [Cruise_Supl_ID], 
[Toursn].[Toursn_Deleted] AS [Toursn_Deleted], 
[Toursn].[Tour_Picture] AS [Tour_Picture], 
[Toursn].[motherTour_ID] AS [motherTour_ID], 
[Toursn].[isMotherTour] AS [isMotherTour], 
[Toursn].[Tour_cruise_before_day] AS [Tour_cruise_before_day], 
[Toursn].[Tour_Thumbnail] AS [Tour_Thumbnail], 
[Toursn].[MainNotification] AS [MainNotification], 
[Toursn].[Operated_Supl_ID] AS [Operated_Supl_ID], 
[Toursn].[TransferStatus] AS [TransferStatus], 
[Toursn].[Escor] AS [Escor], 
[Toursn].[OnList] AS [OnList], 
[Toursn].[PicUploadDate] AS [PicUploadDate], 
[Toursn].[TransCat] AS [TransCat], 
[Toursn].[TransferNo] AS [TransferNo], 
[Toursn].[TransferDuration] AS [TransferDuration], 
[Toursn].[DeparTime] AS [DeparTime], 
[Toursn].[ArrivTime] AS [ArrivTime], 
[Toursn].[Educational] AS [Educational], 
[Toursn].[Tour_Picture_AltTag] AS [Tour_Picture_AltTag], 
[Toursn].[OnlyBookingAgent] AS [OnlyBookingAgent], 
[Toursn].[DuplicateDate] AS [DuplicateDate], 
[Toursn].[Duplicate] AS [Duplicate], 
[Toursn].[DuplicateNo] AS [DuplicateNo], 
[Toursn].[Toursn_CruiseCnt] AS [Toursn_CruiseCnt]
FROM [dbo].[Toursn] AS [Toursn]) AS [Extent1]
    WHERE ([Extent1].[Tour_ID] = @p__linq__0) AND (@p__linq__0 IS NOT NULL)
)  AS [Limit1]',N'@p__linq__0 int',@p__linq__0=25

I cant understand why it is happened? can any one help me with this issue?

Answer 1

thanks every one. i found the problem. may be it was my mistake but i was not create database so i missed that tours table does not have Primary Key.

i assign Tour_ID field as a Primary Key and it was worked nicely.