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Don Burleson Blog 







Natural vs surrogate keys for Oracle tables

Oracle Database Tips by Donald BurlesonMay 7, 2015

Question:  I am designing a database and I need to understand the relative advantages of using natural primary/foreign keys vs using surrogate leys (Oracle sequences).  Can you list the costs benefits of the natural key vs a surrogate key in an Oracle table.

Answer:  First, tp review, a "natural" key is a key that already exists within a table (such as the Social Security Nunber of a person, while s surrogate key has no business meaning and is a unique number generated by an Oracle "sequence".  The choice if a natural vs a surrogate key is straightforward and it depends on these characteristics of the natural key:

Size of natural key:  A surrogate key is a replication, and while small, it takes disk space.  A generated key (an Oracle sequence) is an integer number and takes very little disk space to replicate as a foreign key.

Volatility of natural key:  If the natural key changes frequently, the resulting changes to foreign keys cause changes to index orders and row relocation.  An excellent example of a natural key is a Stock-Keeping Unit (a SKU) that is generally small, static and unique.

Uniqueness of natural key:  To be effective and keep the database flexible, a primary key should be truly unique.  In most vases, even key values such as social security number and problematic (because foreigners do not have an SSN)

In sum, natural keys may be appropriate then you have small, rarely changing, unique values (such as lookup tables), while surrogate keys are desirable for large, highly changing data key columns with duplicate key values (like "people" tables).

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