January 2008
Intermediate to advanced
384 pages
8h 1m
English
Content preview from Joe Celko's Thinking in Sets: Auxiliary, Temporal, and Virtual Tables in SQL
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Chapter 5. Auxiliary Tables
AUXILIARY TABLES HOLD information that is not part of the data model but is needed by the system to work. They are used in queries rather than just providing a simple lookup, as discussed in the last chapter.
Again, the primary key of an auxiliary table is never an identifier; an identifier is unique in the schema and refers to one entity anywhere it appears. As an example of an identifier, your automobile’s VIN is constant, no matter where you park the car, who owns it, what database it is in, or anything else.
An auxiliary table’s primary key is a set of one or more parameters for the function it models. We will discuss this in detail in Chapter 8.
These tables are an alternative to computations and procedural code. ...
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