TSQL Inner select using outer join - sql-server

Question

I have a query that is working for the most part until I had to add the inner select for "Trainers".
As you can see in the code below, I am trying to get all of the trainers for each of the segment ID's.
I am getting an error on the first inner selects where clause WHERE trn.segmentID = tes.teSegmentID saying that tes.teSegmentID is not defined.
Is there another way to approach this query in order to get the trainers like I am trying to accomplish?
SELECT *,
(SELECT e2.[FirstName] AS trainerFirst,
e2.[LastName] AS trainerLast
FROM BS_Training_Trainers AS trn
LEFT OUTER JOIN
employeeTable AS e2
ON trn.trainerEmpID = e2.EmpID
WHERE trn.segmentID = tes.teSegmentID
FOR XML PATH ('trainer'), TYPE, ELEMENTS, ROOT ('trainers'))
FROM dbo.BS_TrainingEvents AS a
WHERE a.trainingEventID IN (SELECT tes.trainingEventID
FROM dbo.BS_TrainingEvent_Segments AS tes
INNER JOIN
dbo.BS_TrainingEvent_SegmentDetails AS tesd
ON tesd.segmentID = tes.teSegmentID
INNER JOIN
dbo.BS_LocaleCodes AS locale
ON locale.localeID = tesd.localeID
WHERE locale.location = 'Baltimore');

Answer 1

It seems like you're taking the scenic route towards this:
SELECT a.*,
X.[FirstName],
X.[LastName]
FROM dbo.BS_TrainingEvents AS a
LEFT OUTER JOIN (SELECT e2.[FirstName], e2.[LastName], locale.location FROM dbo.BS_TrainingEvent_Segments AS tes
INNER JOIN dbo.BS_Training_Trainers AS trn ON trn.segmentID = tes.teSegmentID
INNER JOIN dbo.BS_TrainingEvent_SegmentDetails AS tesd ON tesd.segmentID = tes.teSegmentID
INNER JOIN dbo.BS_LocaleCodes AS locale ON locale.localeID = tesd.localeID
LEFT OUTER JOIN employeeTable AS e2 ON trn.trainerEmpID = e2.EmpID) AS X ON a.trainingEventID = X.trainingEventID
WHERE X.location = 'Baltimore';
Not sure if I got all those joins right, it was hard to decode from all the nesting you have going on.

Answer 2

If I have guessed table relationships from their names correctly, the only way to solve this is to reference the same filtering condition twice: first, in the XML generation part, and second in the outer level of the query:
with cte as (
select distinct tes.trainingEventID, tes.teSegmentID
from dbo.BS_TrainingEvent_Segments AS tes
INNER JOIN dbo.BS_TrainingEvent_SegmentDetails AS tesd ON tesd.segmentID = tes.teSegmentID
INNER JOIN dbo.BS_LocaleCodes AS locale ON locale.localeID = tesd.localeID
WHERE locale.location = 'Baltimore'
)
SELECT a.*, (
SELECT e2.[FirstName] AS trainerFirst, e2.[LastName] AS trainerLast
FROM BS_Training_Trainers AS trn
LEFT OUTER JOIN employeeTable AS e2 ON trn.trainerEmpID = e2.EmpID
inner join cte c on trn.segmentID = c.teSegmentID
FOR XML PATH ('trainer'), TYPE, ELEMENTS, ROOT ('trainers')
)
FROM dbo.BS_TrainingEvents AS a
where exists (select 0 from cte c where c.testrainingEventID = a.trainingEventID);
It's difficult to tell whether this is completely correct, of course, but I hope you get the idea.
Oh yes, and if you would have an event with multiple Baltimore segments, you will never be able to tell which trainer takes which one. But you can always add more data into XML to resolve this.