The Case Against Compound/Natural Keys
- From: "Don Seiler" <don@xxxxxxxxx>
- To: oracle-l <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 26 Jan 2007 22:48:52 -0600
I've been on a crusade against my developers lately after having had
enough of fields being added to already-insane primary keys.
Today I was given a script to add a field to make what is now a
15-field primary key, all natural data. The first 9 fields of the key
also provide the foreign key into the parent table (although a foreign
key constraint is, of course, not used), and it carries on down the
line, growing worse and worse. They've all heard me calling for
surrogate keys, but they say they need uniqueness among this set of
fields. Then when they discover duplicates, they just add another
field.
I even suggested having NO primary key, just a non-unique key on the
first 4 or 5 fields. But again they say they need to guarantee
uniqueness. These tables are bulk-loaded and can contain over 150
million records. There is no query that even comes close to utilizing
these fields, it is purely a unique constraint. However, since a
unique constraint also creates an index, I didn't see any advantage
there.
I'm looking for the words to basically doom this practice once and for
all. I've already told them about the degradation of normalization,
the storage needed for these unused indexes, etc. They claim there's
nothing they can do for now. Migrating to surrogate keys would be
non-trivial and isn't a priority, it seems.
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