Primary key
Each table can have, at most, a single primary key constraint. The primary key
may consist of more than one column in a table.
The primary key constraint forces each primary key to have a unique value. It
enforces both the unique constraint and the NOT NULL constraint. A primary
key constraint will create a unique index, if one doesn??™t already exist for the
specified column(s).
Should You Normalize Your Data?
Whenever possible, we recommend that yougo through the process of designing a normalized
structure for your database.
Data normalization has been proven, both theoretically and in decades of practice, to
provide concrete benefits. In addition, the process of creating a normalized data design
is intimately intertwined with the process of understanding the data requirements for
your application system. You can improve even the simplest database by the discoveries
made during the process of normalization.
However, there may be times when youfeel that the benefits of a fully normalized
design will counteract the performance penalty that a design imposes on your production
systems.
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