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Don Burleson Blog 







Oracle Surrogate Key Tips

Expert Oracle Database Tips by Donald BurlesonMarch 29, 2015


Question:  :  I have a hospital database where the patient ID does not immediately exist when a patient first calls for an appointment.   I have a person table and an appointment tables, and each appointment must be tied to a person.   How to I create a good candidate key until I can generate the correct primary key for the row?

Answer:  As you know, referential integrity (RI) is used to enforce entity relationships, such as that between parent and child tables.

For example, a customer table may place many orders, but each order only belongs to one customer.

You want a candidate key, a unique secondary key which can be used as a surrogate to the primary key . . .

When the primary key may not be available immediately, you can use a surrogate key to enforce the business relationship.

Dr. Ralph Kimball makes a compelling argument for using surrogate keys, primarily to improve database performance:  

?Replacing big, ugly natural keys and composite keys with beautiful, tight integer surrogate keys is bound to improve join performance.

The storage requirements are reduced, and the index lookups would seem to be simpler.  

I would be interested in hearing from anyone who has harvested a performance boost by replacing big ugly fat keys with anonymous integer keys.?

Your case is a perfect example, where a patient ID may not exist when the first appointment is made.

A surrogate key can be a system generated sequence number or a combination of parts of a column that serve to make the row unique.

For example, there may be surrogate keys:

  •  The first five letters of the last name concatenated with the date of birth: burle121248
  •  The persons initials concatenated with the first 4 digits of their social security number: dkb4645

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, you cannot enforce this if you leave orphan appointments, which are not hooked to a parent row . . . so you need a surrogate key!

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

For example, 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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