SQL Aggregate functions with groupings - sql

Question

I need to create some checks to make sure that students are enrolled in the correct courses with the correct number of units. Here is my SQL at the moment.
SELECT StudentID
,AssessmentCode
,BoardCode
,BoardCategory
,BoardUnits
,sum(cast(boardunits as int)) over (partition by studentid,boardcategory) as UnitCount
,Count(boardcategory) over (partition by studentid) as SubjectCount
FROM uvNCStudentSubjectDetails
where fileyear = 2015
and filesemester = 1
and studentyearlevel = 11
and StudentIBFlag = 0
order by Studentnameinternal,BoardCategory
This gives me the following info...
StudentID AssessmentCode BoardCode BoardCategory BoardUnits UnitCount SubjectCount
61687 11TECDAT 11080 A 2 11 7
61687 11PRS1U 11350 A 1 11 7
61687 11MATGEN 11235 A 2 11 7
61687 11LANGRB 11870 A 2 11 7
61687 11ENGSTD 11130 A 2 11 7
61687 11GEOGEO 11190 A 2 11 7
64549 11TECIND 11200 A 2 10 7
64549 11SCIPHY 11310 A 2 10 7
64549 11SCIEAE 11100 A 2 10 7
64549 11MATGEN 11235 A 2 10 7
64549 11ENGSTD 11130 A 2 10 7
64549 11TECHOS 26501 B 2 2 7
64549 11MUSDRS 63212 C 1 1 7
45461 11ECOECO 11110 A 2 13 7
45461 11ENGADV 11140 A 2 13 7
45461 11HISMOD 11270 A 2 13 7
45461 11HISLST 11220 A 2 13 7
45461 11MATMAT 11240 A 2 13 7
45461 11PRS1U 11350 A 1 13 7
45461 11SCIBIO 11030 A 2 13 7
Note for the first student, I have a count of Category A subject Units (11 in total) He is only doing Category A subjects. For the second student, he has 10 units of Category A subjects, he is doing 1 Category B subject worth 2 units and one category C subject worth 1 unit. the final student just has 13 Category A units.
Now what I would really like is something like this...!
StudentID Sum A Units Sum B Units Sum C Units Sum A Units + Sum B Units Count of Subjects
61687 11 0 0 11 7
64549 10 2 1 12 7
45461 13 0 0 13 7
So I would like some aggregated functions with a student grouped onto only 1 row and the sum of his different units as separate fields. I would also like a field which sums the Category A and B Units and also a field which gives a count of the total number of subjects they are doing. I could then use this data to set up some warning messages if a student is not doing the correct number of A or B Units etc
I have played around with common table expressions, subqueries etc but am not really sure what I am doing and am not sure which is the correct way about getting the data in the form I want.
Is anyone able to help?

Answer 1

SELECT
STUDENTID,
SUM(CASE BOARDCATEGORY WHEN 'A' THEN 1 ELSE 0 END) AS SUM_A_UNITS,
SUM(CASE BOARDCATEGORY WHEN 'B' THEN 1 ELSE 0 END) AS SUM_B_UNITS,
SUM(CASE BOARDCATEGORY WHEN 'C' THEN 1 ELSE 0 END) AS SUM_C_UNITS,
SUM(CASE BOARDCATEGORY WHEN 'A' THEN 1 WHEN 'B' THEN 1 ELSE 0 END) AS SUM_A_UNITS+SUM_B_UNITS,
COUNT(BOARDCODE) AS COUNT_OF_SUBJECTS
FROM (
SELECT StudentID
,AssessmentCode
,BoardCode
,BoardCategory
,BoardUnits
,sum(cast(boardunits as int)) over (partition by studentid,boardcategory) as UnitCount
,Count(boardcategory) over (partition by studentid) as SubjectCount
FROM uvNCStudentSubjectDetails
where fileyear = 2015
and filesemester = 1
and studentyearlevel = 11
and StudentIBFlag = 0
order by Studentnameinternal,BoardCategory
)
GROUP BY STUDENTID;
Wrapped your SQL statement in the solution, so that you can see what the solution does straight away.
Use SUM and CASE (i.e. SUM only when a condition is met).