Data Retrieval
SQL is based on mathematical principles, specifically set theory and relational algebra. The data is stored in the database as unordered sets of data records. SQL is a set-oriented language and many of its language elements are directly related to relational algebraic terms, such as permutation, projection, restriction, and join.
A set of data is represented in a DB2 database as a table or a view and is stored in a DB2 table without regard to order. To retrieve data in a particular order, an ORDER BY phrase must be added to a SELECT statement. Similarly, if the data is to be grouped, then a GROUP BY phrase must be added to the statement.
Many of the examples that are used in this chapter are based on the employee table from the ...
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