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Asked: 2026-05-16T08:53:52+00:00

I’m developing a data warehouse and have come up against a problem I’m not

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I’m developing a data warehouse and have come up against a problem I’m not sure how to fix. The current schema is defined below:

DimInstructor <- Dimension table for instructors
DimStudent <- Dimension table for students

I want to implement a scenario whereby if details of an instructor change in my OLTP database, I want to add a new record in the DimInstructor table for historical reporting reasons.

Now, I’m wanting to create a lesson dimension table called DimLesson. In DimLesson I want to create a reference to the instructor.

The DimInstructor table contains:

InstructorDWID <- Identity field when entered into DW
InstructorID <- The instructor ID that has come from the OLTP database

Now, I can’t make InstructorID a primary key because it isn’t guaranteed to be unique (if the instructor changes their name, there will be 2 records in the DW with the same InstructorID value).

So my question is, how do I reference the instructor from DimLesson? Do I use the InstructorDWID? If so, should I have 2 entries for an instructor in DimInstructor, it would make queries more complicated when I’m wanting to look at all lessons by a specific instructor.

Any help would be appreciated!

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1 Answer

  1. Editorial Team

    Paul,

    There are multiple ways you can handle this. You can use an effective date/inactive date, sequence number or a version number to differentiate the records with the same InstructorID.

    The DIM that captures all relevant details would be like..

    create table DIM_INSTRUCTOR(
  instr_guid number, --populated through a sequence     -----Composite pk-Part1
  istr_oid   number, --direct id from the OLTP system   -----cmposite  pk-part2
  instr_name number,
  other_attr varchar2(25),
  eff_date   date,
  expiration_date date
);

    instr_guid is directly generated from a sequence and is independent of the OLTP system.

    This would let you capture all the details for a given instructor.
    You can use just the instr_guid as the foreign key to the fact table, but including both of them (instr_guid,instr_guid) would increase the ease of querying .. which is one of the goals of Datawarehousing.

    Useful Links:

    http://en.wikipedia.org/wiki/Surrogate_key
    http://en.wikipedia.org/wiki/Slowly_changing_dimension#Type_2

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