SQL select statement nested sub queries

Question

I am having trouble wrapping my brain around a nested sub query in a select sql statement. Basically what I have here works fine, but there definitely must be a way to make this query more dynamic and elegant than the current setup below:

    SELECT Jobs.JobID, Jobs.JobName, 
    (

            SELECT COALESCE(SUM(JobQualifiers.Weight), 0)   
            FROM Jobs j1
            INNER JOIN 
            JobQualifiers ON j1.JobID = JobQualifiers.JobID 
            INNER JOIN  
            Qualifications ON Qualifications.QualificationID = JobQualifiers.QualificationID
            INNER JOIN
            SubGroupQualifiers sgq ON Qualifications.QualificationID = sgq.QualificationID
            INNER JOIN
            QualificationSubGroups ON QualificationSubGroups.QualificationSubGroupID = sgq.SubGroupID
        WHERE 
            j1.JobID = Jobs.JobID
            AND
            QualificationSubGroups.QualificationSubGroupID = 6

    ) as SubGroup6,
    (

            SELECT 
            COALESCE(SUM(JobQualifiers.Weight), 0)
            FROM Jobs j2
            INNER JOIN 
            JobQualifiers ON j2.JobID = JobQualifiers.JobID 
            INNER JOIN  
            Qualifications ON Qualifications.QualificationID = JobQualifiers.QualificationID
            INNER JOIN
            SubGroupQualifiers sgq ON Qualifications.QualificationID = sgq.QualificationID
            INNER JOIN
            QualificationSubGroups ON QualificationSubGroups.QualificationSubGroupID = sgq.SubGroupID
        WHERE 
            j2.JobID = Jobs.JobID
            AND
            QualificationSubGroups.QualificationSubGroupID = 7

    ) as SubGroup7,
(

        SELECT COALESCE(SUM(JobQualifiers.Weight), 0)   
        FROM Jobs j3
        INNER JOIN 
        JobQualifiers ON j3.JobID = JobQualifiers.JobID 
        INNER JOIN  
        Qualifications ON Qualifications.QualificationID = JobQualifiers.QualificationID
        INNER JOIN
        SubGroupQualifiers sgq ON Qualifications.QualificationID = sgq.QualificationID
        INNER JOIN
        QualificationSubGroups ON QualificationSubGroups.QualificationSubGroupID = sgq.SubGroupID
    WHERE 
        j3.JobID = Jobs.JobID
        AND
        QualificationSubGroups.QualificationSubGroupID = 8

) as SubGroup8
FROM Jobs

My goal here is to make the subquery selection dynamic instead of hardcoded to a QualificationSubGroups.QualificationSubGroupID with Subgroup6, SubGroup7, SubGroup8 etc. I believe I need a nested subquery, but how to implement it is beyond me. This may be incredibly ambiguous of a description so I'd be happy to give more detail as needed! Thanks ahead for any responses.

Answer 1

Instead of multiple subselects you could use conditional aggregation, something like:

SELECT    j.JobID
        , j.JobName
        , COALESCE(SUM(CASE WHEN qsg.QualificationSubGroupID = 6 THEN jq.Weight END), 0)
        , COALESCE(SUM(CASE WHEN qsg.QualificationSubGroupID = 7 THEN jq.Weight END), 0)
        , COALESCE(SUM(CASE WHEN qsg.QualificationSubGroupID = 8 THEN jq.Weight END), 0)
FROM Jobs j
INNER JOIN JobQualifiers jq ON j.JobID = jq.JobID
INNER JOIN Qualifications q ON q.QualificationID = jq.QualificationID
INNER JOIN SubGroupQualifiers sgq ON q.QualificationID = sgq.QualificationID
INNER JOIN QualificationSubGroups qsg ON qsg.QualificationSubGroupID = sgq.SubGroupID
WHERE qsg.QualificationSubGroupID IN (6,7,8)
GROUP BY j.JobID
       , j.JobName

Answer 2

I am not sure exactly what you are trying to do but you can try like below using a CASE condition

SELECT Jobs.JobID, Jobs.JobName,
CASE WHEN QualificationSubGroups.QualificationSubGroupID = 6
THEN COALESCE(SUM(JobQualifiers.Weight), 0) END as SubGroup6,
CASE WHEN QualificationSubGroups.QualificationSubGroupID = 7
THEN COALESCE(SUM(JobQualifiers.Weight), 0) END as SubGroup7,
CASE WHEN QualificationSubGroups.QualificationSubGroupID = 8
THEN COALESCE(SUM(JobQualifiers.Weight), 0) END as SubGroup8
FROM Jobs j1
INNER JOIN 
JobQualifiers ON j1.JobID = JobQualifiers.JobID 
INNER JOIN  
Qualifications 
ON Qualifications.QualificationID = JobQualifiers.QualificationID
INNER JOIN
SubGroupQualifiers sgq 
ON Qualifications.QualificationID = sgq.QualificationID
INNER JOIN
QualificationSubGroups 
ON QualificationSubGroups.QualificationSubGroupID = sgq.SubGroupID