Chapter 4. Query Optimization
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 query to retrieve rows from a table, you get back another set of rows and columns. 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.
The real world, of course, is quite different. Database management systems implement abstract concepts but do so on real ...
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