EF6 - Generating unneeded nested queries - sql-server

Question

I have the following tables:
MAIN_TBL:
Col1 | Col2 | Col3
------------------
A | B | C
D | E | F
And:
REF_TBL:
Ref1 | Ref2 | Ref3
------------------
A | G1 | Foo
D | G1 | Bar
Q | G2 | Xyz
I wish to write the following SQL query:
SELECT M.Col1
FROM MAIN_TBL M
LEFT JOIN REF_TBL R
ON R.Ref1 = M.Col1
AND R.Ref2 = 'G1'
WHERE M.Col3 = 'C'
I wrote the following LINQ query:
from main in dbContext.MAIN_TBL
join refr in dbContext.REF_TBL
on "G1" equals refr.Ref2
into refrLookup
from refr in refrLookup.DefaultIfEmpty()
where main.Col1 == refr.Col1
select main.Col1
And the generated SQL was:
SELECT
[MAIN_TBL].[Col1]
FROM (SELECT
[MAIN_TBL].[Col1] AS [Col1],
[MAIN_TBL].[Col2] AS [Col2],
[MAIN_TBL].[Col3] AS [Col3]
FROM [MAIN_TBL]) AS [Extent1]
INNER JOIN (SELECT
[REF_TBL].[Ref1] AS [Ref1],
[REF_TBL].[Ref2] AS [Ref2],
[REF_TBL].[Ref3] AS [Ref3]
FROM [REF_TBL]) AS [Extent2] ON [Extent1].[Col1] = [Extent2].[Ref1]
WHERE ('G1' = [Extent2].[DESCRIPTION]) AND ([Extent2].[Ref1] IS NOT NULL) AND CAST( [Extent1].[Col3] AS VARCHAR) = 'C') ...
Looks like it is nesting a query within another query, while I just want it to pull from the table. What am I doing wrong?

Answer 1

I may be wrong, but it looks like you don't do the same in linq query and sql query, especially on your left joining clause.
I would go for this, if you want something similar to your sql query.
from main in dbContext.MAIN_TBL.Where(x => x.Col3 == "C")
join refr in dbContext.REF_TBL
on new{n = "G1", c = main.Col1} equals new{n = refr.Ref2, c = refr.Col1}
into refrLookup
from r2 in refrLookup.DefaultIfEmpty()
select main.Col1
By the way, it doesn't make much sense to left join on a table which is not present in the select clause : you will just get multiple identical Col1 if there's more than one related item in the left joined table...