SQL Server self referencing query - sql

Question

Please consider the following:
CREATE DATABASE TEST
USE TEST
CREATE TABLE Student
(
StudentID INT IDENTITY
PRIMARY KEY ,
FirstName NVARCHAR(50) ,
LastName NVARCHAR(50)
)
CREATE TABLE StudentComponent
(
StudentComponentID INT IDENTITY
PRIMARY KEY ,
StudentID INT FOREIGN KEY REFERENCES dbo.Student(StudentID) ,
ComponentName NVARCHAR(50) ,
ComponentRef NVARCHAR(50) ,
ComponentType NCHAR(2)
)
CREATE TABLE Component
(
ComponentID INT IDENTITY
PRIMARY KEY ,
StudentComponentID INT FOREIGN KEY REFERENCES dbo.StudentComponent(StudentComponentID) ,
ComponentName NVARCHAR(50) ,
ComponentRef NVARCHAR(50) ,
ComponentType NCHAR(2)
)
I have 3 tables
Student
StudentComponent
Component
split out into dimensions
CREATE TABLE DimClass
(ClassDwKey INT,
ClassName NVARCHAR(50),
ClassRef NVARCHAR(50))
CREATE TABLE DimCollege
(CollegeDwKey INT,
CollegeName NVARCHAR(50),
CollegeRef NVARCHAR(50))
CREATE TABLE DimSubject
(SubjectDwKey INT,
SubjectName NVARCHAR(50),
SubjectRef NVARCHAR(50))
CREATE TABLE DimStudent
(StudentDwKey INT,
StudentName NVARCHAR(50))
INSERT INTO
CREATE TABLE FactAcademicEvent
(StudentDwKey int, ClassDwKey int, CollegeDwKey int, SubjectDwKey INT)
With relationship in same order between them (Student --> StudentComponent --> Component). I have split the components out into their own dimensions, DimClass, DimCollege, DimSubject (split by componenttype field, = 'CL' for class, 'SU' for subject, 'CO' for college etc. I am trying to load a fact table getting my surrogate keys from my dimensions and produce a row with the following
StudentDwKey (from dimstudent), ClassDwKey, CollegeDwKey, SubjectDwKey. There is a link between the dimensions and the component table ComponentKey, which links to student through studentcomponent table.
StudentComponent and Component are basically the same, except StudentComponent references students so has more rows.
Any ideas?

Answer 1

EDIT :
Complete change based on OP's edits and comments.
SELECT
s.StudentID,
MAX(dim_s.StudentDwKey ) AS StudentDwKey,
MAX(dim_cl.ClassDwKey ) AS ClassDwKey,
MAX(dim_su.SubjectDwKey) AS SubjectDwKey,
MAX(dim_co.CollegeDwKey) AS CollegeDwKey
FROM
Student AS s
LEFT JOIN
StudentComponent AS sc
ON sc.StudentID = s.StudentID
LEFT JOIN
dimStudent AS dim_s
ON dim_s.StudentName = s.StudentName -- or whatever is a reliable join
LEFT JOIN
dimClass AS dim_cl
ON dim_cl.ClassRef = sc.ComponentRef
AND sc.ComponentType = 'CL'
LEFT JOIN
dimSubject AS dim_su
ON dim_su.SubjectRef = sc.ComponentRef
AND su.ComponentType = 'SU'
LEFT JOIN
dimCollege AS dim_co
ON dim_co.CollegeRef = sc.ComponentRef
AND sc.ComponentType = 'CO'
GROUP BY
s.StudentID

Answer 2

Keep the student details in the Student table (which you have done) and the component details in the Component table (which you have not done) and use the StudentComponent table to link them together. Something like this:
CREATE DATABASE TEST
USE TEST
CREATE TABLE Student
(
StudentID INT IDENTITY
PRIMARY KEY ,
FirstName NVARCHAR(50) ,
LastName NVARCHAR(50)
)
CREATE TABLE StudentComponent
(
StudentComponentID INT IDENTITY
PRIMARY KEY ,
StudentID INT FOREIGN KEY REFERENCES dbo.Student(StudentID) ,
ComponentID INT FOREIGN KEY REFERENCES dbo.Component(ComponentID),
)
CREATE TABLE Component
(
ComponentID INT IDENTITY
PRIMARY KEY ,
ComponentName NVARCHAR(50) ,
ComponentRef NVARCHAR(50) ,
ComponentType NCHAR(2)
)