By Paul Dubois

Database management systems implement abstract concepts but do so on real hardware bound by real physical constraints. As a result, queries take time—sometimes an annoyingly long time. Find out how to minimize your wait in this sample chapter.

The world of relational database theory is a world dominated by tables and sets, and operations on tables and sets. A database is a set of tables, and a table is a set of rows and columns. When you issue a SELECT statement to retrieve rows from a table, you get back another set of rows and columns—that is, another table. These are abstract notions that make no reference to the underlying representation a database system uses to operate on the data in your tables. Another abstraction is that operations on tables happen all at once; queries are conceptualized as set operations and there is no concept of time in set theory.

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