Database Reference
In-Depth Information
8
Database Redesign
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To understand the need for database redesign
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To be able to use correlated subqueries
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To be able to use the SQL EXISTS and NOT EXISTS
keywords in correlated subqueries
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To understand reverse engineering
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To be able to use dependency graphs
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To be able to change table names
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To be able to change table columns
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To be able to change relationship cardinalities
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To be able to change relationship properties
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To be able to add and delete relationships
As stated in
Chapter 1, database design
and implementation is needed for three reasons.
Databases can be created (1) from existing data (such
as spreadsheets and databases tables), (2) for a new systems
development project, or (3) for a database redesign. We have discussed
the first two sources in Chapters 2 through 7. In this chapter, we will discuss
the last source: database redesign.
We begin with a discussion of the need for database redesign, and then
we will describe two important SQL statements: correlated subqueries and
EXISTS. These statements play an important role when analyzing data prior
to redesign. They also can be used for advanced queries and are important
in their own right. After that discussion, we will turn to a variety of common
database redesign tasks.
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