SQL Queries
This section provides the third perspective on SQL, an introduction to the SQL querying language. The querying part of SQL is the visible portion of an iceberg whose bulky mass is hidden from view. The hidden portion is the data management side of the language—the definitions of tables and views, inserting rows, updating rows, defining triggers, stored procedures, and so on. As data miners and analysts, our goal is to exploit the visible part of the iceberg, by extracting useful information from the database.
SQL queries answer specific questions. Whether the question being asked is actually the question being answered is a big issue for database users. The examples throughout this book include both the question and the SQL that answers it. Sometimes, small changes in the question or the SQL produce very different results.
What to Do, Not How to Do It
A SQL query describes the result set, but does not specify how this is accomplished. This approach has several advantages...