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Last Modified: 2015-12-09
I have a classroom table.  It has a primary key column, along with primary teacher Foreign key,  secondary teacher Foreign key and tertiary teacher Foreign key.  Each of the teacher FKs are keys to a user table.

A teacher could be primary in one room, secondary in another and tertiary in a third.  So, I need a query that returns the Primary Key of the classroom for a teacher, based on the primary, secondary and tertiary hierarchy.   For this example I would want the Primary Key of the classroom where they are the primary teacher.  

If the teacher was not a primary teacher in any classroom, but was secondary teacher in one room and tertiary in a second room, then I need the Primary Key of the classroom where they are the secondary teacher.  

classroom Data examples

classroom ID       FKPrimary       FKSecondary         FKTertiary
1                                  100                    NULL                     NULL
2                                  200                     1234                     400
3                                  300                     400                       500
4                                  400                     300                       200  
5                                  500                     400                       4444
                               

For teacher 100, I need classroom ID of 1.
For teacher 200, I need classroom ID of 2.
For teacher 300, I need classroom ID of 3.
For teacher 400, I need classroom ID of 4.
For teacher 500, I need classroom ID of 5.

For teacher 1234, I need classroom ID of 2.
For teacher 4444, I need classroom ID of 5.
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