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Don Burleson Blog 







Oracle Candidate Key Tips

Expert Oracle Database Tips by Donald BurlesonMarch 23, 2015


Question:  I have a situation where I need to apply referential integrity (RI) to specific data.  In this case, selected rows of a given column will contain the reference key to the primary key of a different table.  The problem is that the reference column is not mandatory for all rows.  When the reference column is NULL, it should not be referred by the parent table.

For example, in a telephonic appointment form, a patient may make an appointment even if they do not know their user id assigned by the hospital.  The user id field would be null, but the name is entered manually into the record; however, in the event the user id is entered, it needs to fetch the patient name from the master table.

Is there a solution for this problem?

Answer:  This can be accomplished with a candidate key.

Referential Integrity (RI) is used to enforce entity relationships between tables.

One example of such a relationship might be that a customer may place many orders, but each order only belongs to one customer.

In your situation, there is a one-to-many between patients and appointments:

  • each patient may have many appointments

  • each appointment is for one and only one patient

Obviously, this relationship cannot be enforced if you leave "orphan" appointments, which are not hooked to a patient.

Since the patients using your system may not know their user id assigned by the hospital, you need a candidate key.

The candidate key can either be made up, like an Oracle sequence, or it can be a unique combination of information you do have.

In your case, you may not know the hospital userID, but you can make a unique name from the first 5 letters of the last name concatenated with the date of birth, something like this:

Sam Jones, born 3/13/1950
key - jones3131950

I have a good book on Oracle Design that might help.


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