Lessons Learned
This chapter introduces SQL and relational databases from several different perspectives that are important for data mining and data analysis. The focus is exclusively on using databases to extract information from data, rather than on the mechanics of building databases, the myriad options available in designing them, or the sophisticated algorithms implemented by database engines.
One very important perspective is the data perspective—the tables themselves and the relationships between them. Entity-relationship diagrams are a good way of visualizing the structure of data in the database and the relationships among tables. Along with introducing entity-relationship diagrams, the chapter also explains the various datasets used throughout this book.
Of course, tables and databases store data, but they don’t actually do anything. Queries extract information, transforming data into information. For some people, thinking in terms of data flow diagrams is simpler...