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Control the Sql that Linq sends to db explanation

Hello I have the a linq query that I have created for a left outer join. I am wondering why linq creates the Sql it does, and how to make it a better query.
here's the c# query:
var query=
(
from subject in subjects
join statement in statements.DefaultIfEmpty() on subject.Id equals statement.SubjectId
select subject
);
query.Take(100).Dump();
and the Sql that it sends:
SELECT TOP (100)
--some fields here
FROM [Subject] AS [t0]
INNER JOIN ((
SELECT NULL AS [EMPTY]
) AS [t1]
LEFT OUTER JOIN [SubjectStatement] AS [t2] ON 1=1 ) ON [t0].[id] = [t2].[SubjectId]
What I would like to see sent is
SELECT TOP(100)
--some fields here
FROM Subject
LEFT OUTER JOIN SubjectStatemnt ON Subject.Id = SubjectStatement.Id
Is there a way to control the Sql that is being passed to Sql Server?

You are using the syntax of an inner join and while that might work out some times, you would normally create a left join using the following syntax:
var query =
(
from subject in subjects
join statement in statements on subject.Id equals statement.SubjectId into ljStatement
from statement in ljStatement.DefaultIfEmpty()
select subject
);
query.Take(100).Dump();
This would result in:
SELECT TOP (100) [t0].[Id]
FROM [Subject] AS [t0]
LEFT OUTER JOIN [SubjectStatement] AS [t1] ON [t0].[Id] = [t1].[SubjectId]
into (C# Reference)
The into contextual keyword can be used to create a temporary
identifier to store the results of a group, join or select clause into
a new identifier.
join clause (C# Reference)
A join clause with an into expression is called a group join.
...
A group join produces a hierarchical result sequence, which associates elements in the left source sequence with one or more matching elements in the right side source sequence. A group join has no equivalent in relational terms; it is essentially a sequence of object arrays.
If no elements from the right source sequence are found to match an element in the left source, the join clause will produce an empty array for that item. Therefore, the group join is still basically an inner-equijoin except that the result sequence is organized into groups.

OleDB JOIN Syntax Not Correct

I recently asked a question on StackOverflow (MySQL Returns All Rows When field = 0) regarding a query statement not working in MySQL. I now have a very similar problem, this time using OleDB where I am trying to use a join to include fields that have 0 as an entry, but not select every field in the table as a result.
The new look MySQL query posted in the above question as the accepted answer works without a hitch. However the OleDB counterpart I have written to do almost the same does not. It's a bit messy as the tables are not named very well (I didn't create this database) and I'm getting a simple syntax error;
myQuery.CommandText = "SELECT s.scm_num, s.scm_name, c.cr3_text, q.qsp_value, s.scm_bprefix, s.scm_nxbnum FROM qspreset q INNER JOIN sdccomp s LEFT OUTER JOIN cntref3 c ON s.scm_cntref3=c.cr3_id AND q.qsp_relat=s.scm_invtype AND q.qsp_what=13";
I'm querying another table here as well as the two involved in the LEFT OUTER JOIN and I believe that is where I am making the mistake.

Join conditions need to be with the join
myQuery.CommandText =
"SELECT s.scm_num, s.scm_name, c.cr3_text, q.qsp_value, s.scm_bprefix, s.scm_nxbnum
FROM qspreset q
INNER JOIN sdccomp s
on q.qsp_relat = s.scm_invtype AND q.qsp_what = 13
LEFT OUTER JOIN cntref3 c
ON s.scm_cntref3 = c.cr3_id";
q.qsp_what = 13 can be moved to a where
I happen to like this style
In the case of MSSQL T-SQL and some queries with a lot of joins I have gotten more efficient query plan by moving a where condition up into a join. The filter happened early rather that last.
If you don't believe you can put a hard value in a join see SQLfiddle

EF Ignores Eager-Loading "Include" statement

I've seen this issue come up again and again and again. As I read through the answers, the common-ish answer is summarized well by this statement:
any manual join or projection will change the shape of the query and Include will not be used
-Ladislav Mrnka
Ok, so I decided to make a "hello world" sample EF code-first project with DbContext that would test that statement. I created the following query:
var result =
from c in context.Customers.Include(i => i.Addresses)
from a in c.Accounts
where a.ID > 4
select c;
The Include() statement should work, because I'm clearly meeting the requirements: (1) I am not modifying the projection by using an anonymous type and (2) I am not manually handling the joins.
Nevertheless, it doesn't work. The SQL query generated by this query is this:
SELECT
[Extent1].[ID] AS [ID],
[Extent1].[Name] AS [Name]
FROM [dbo].[Customers] AS [Extent1]
INNER JOIN [dbo].[Accounts] AS [Extent2] ON [Extent1].[ID] = [Extent2].[Customer_ID]
WHERE [Extent2].[ID] > 4
If I remove the join and filtering on the Accounts, then the include statement is correctly generated. Why is this happening?
I'm also bothered that EF official documentation doesn't seem to explain the rules of when Include() is or is not honored. Did I simply overlook something?

In a way you are "manually handling a join" by specifying the second from statement with c.Accounts.
Try the below query, whose context is solely based on a Customer entity:
from c in context.Customers.Include( i => i.Addresses )
where c.Accounts.Any( a => a.ID > 4 )
select c

Too Many Left Outer Joins in Entity Framework 4? [duplicate]

This question already has answers here:
Simple Linq query has duplicated join against same table?
(3 answers)
Closed 3 years ago.
I have a product entity, which has 0 or 1 "BestSeller" entities. For some reason when I say:
db.Products.OrderBy(p => p.BestSeller.rating).ToList();
the SQL I get has an "extra" outer join (below). And if I add on a second 0 or 1 relation ship, and order by both, then I get 4 outer joins. It seems like each such entity is producing 2 outer joins rather than one. LINQ to SQL behaves exactly as you'd expect, with no extra join.
Has anyone else experienced this, or know how to fix it?
SELECT
[Extent1].[id] AS [id],
[Extent1].[ProductName] AS [ProductName]
FROM [dbo].[Products] AS [Extent1]
LEFT OUTER JOIN [dbo].[BestSeller] AS [Extent2] ON [Extent1].[id] = [Extent2].[id]
LEFT OUTER JOIN [dbo].[BestSeller] AS [Extent3] ON [Extent2].[id] = [Extent3].[id]
ORDER BY [Extent3].[rating] ASC

That extra outer join does seem quite superfluous. I think it's best to contact the entity framework design team. They may know if it's a bug and see if it something that needs to be resolved in a next version. You can contact them at Link

It may be a bug, but it seems like such a simple example that it is strange that the bug has not been caught and fixed.
Could you check your EF model.
Has the BestSeller table been added twice, or is there a duplication in the relationship between the tables.

Eager loading with HQL

Is it possible to do eager loading with HQL without touching mappings? The "left join fetch" expression is completely ignored by nHibernate.
var query = Session.CreateQuery("from o in Member left join fetch o.Photos");
query.List<Member>();
The generated SQL is
SELECT this_.Id as Id7_1_, this_.Name as Name7_1_, this_.AltNames as AltNames7_1_,
this_.Tags as Tags7_1_, this_.Loved as Loved7_1_, profile2_.id as id6_0_,
profile2_.Website as Website6_0_, profile2_.Email as Email6_0_,
profile2_.Shop as Shop6_0_
FROM Member this_
left outer join member_profile profile2_ on this_.Id=profile2_.id
limit 10;
And then 10 statements grabbing the photos. MemberProfile is mapped as OneToOne.

You could use the fetch keyword:
from Cat as cat inner join fetch cat.Mate
This will eagerly load the Mate association.