We are now at a point in this book where my professional career started, working with databases and SQL. Structured Query Language (SQL) was created decades ago as a means to communicate with structured data stored in tables. Over the years, SQL has evolved from multiple variations that were specific to the underlining database technology. For example, IBM, Oracle, and Sybase all had variations in their SQL commands, which built loyalty in their customers but required changes when switching vendors. The adoption of the International Organization for Standardization (ISO) and American National Standards Institute (ANSI) standards helped to define what is commonly used today.
So far in this book, all of the examples of structured data focused on one table or file. Relational databases solve the problem of storing data together in multiple tables while keeping consistency across them using the concept of a primary and foreign key...
