Before you rush off and start normalizing everything, a word of
warning. No process is better than good old common sense. Take a
look at this example.
Customer table
Number - primary key
Name
Address
Zip Code
Town
What normal form is this table in? Giving it a quick glance, we
see no repeating groups, and a primary key defined, so it's at
least in 1st normal form. There's only one key, so we needn't even
look for partial dependencies, so it's at least in 2nd normal form.
How about transitive dependencies? Well, it looks like Town might
be determined by Zip Code. And in most parts of the world
that's usually the case. So we should remove Town, and place it
in a separate table, with Zip Code as the key? No! Although this
table is not technically in 3rd normal form, removing this
information is not worth it. Creating more tables increases the
load slightly, slowing processing down. This is often counteracted
by the reduction in table sizes, and redundant data. But in this
case, where the town would almost always be referenced as part
of the address, it isn't worth it. Perhaps a company that uses the data to
produce regular mailing lists of thousands of customers should normalize
fully. It always comes down to how the data is
going to be used. Normalization is just a helpful process that
usually results in the most efficient table structure, and not a
rule for database design. But judging from some of the table
structures I've seen out there, it's better to err and normalize
than err and not!
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