In the early 1970s, an IBM research fellow named Dr. E. F. Codd endeavored to apply the rigors of mathematics to the then-untamed world of data storage and retrieval. Codd's work led to the definition of the relational data model and a language called DSL/Alpha for manipulating data in a relational database. IBM liked what they saw, so they commissioned a project called System/R to build a prototype based on Codd's work. Among other things, the System/R team developed a simplified version of DSL called SQUARE, which was later renamed SEQUEL, and finally renamed SQL.
The work done on System/R eventually led to the release of various IBM products based on the relational model. Other companies, such as Oracle, rallied around the relational flag as well. By the mid 1980s, SQL had gathered sufficient momentum in the marketplace to warrant oversight by the American National Standards Institute (ANSI). ANSI released its first SQL standard in 1986, followed by updates in 1989, 1992, 1999, and 2003. There will undoubtedly be further refinements in the future.
Thirty years after the System/R team began prototyping a relational database, SQL is still going strong. While there have been numerous attempts to dethrone relational databases in the marketplace, well-designed relational databases coupled with well-written SQL statements continue to succeed in handling large, complex data sets where other methods fail.
Given that Oracle was an early adopter of the relational model and SQL, one might think that they would have put a great deal of effort into conforming with the various ANSI standards. For many years, however, the folks at Oracle seemed content that their implementation of SQL was functionally equivalent to the ANSI standards without being overly concerned with true compliance. Beginning with the release of Oracle8i, however, Oracle has stepped up its efforts to conform to ANSI standards and has tackled such features as the CASE statement and the left/right/full outer join syntax.
Ironically, the business community seems to be moving in the opposite direction. A few years ago, people were much more concerned with portability and would limit their developers to ANSI-compliant SQL so that they could implement their systems on various database engines. Today, companies tend to pick a database engine to use across the enterprise and allow their developers to use the full range of available options without concern for ANSI-compliance. One reason for this change in attitude is the advent of n-tier architectures, where all database access can be contained within a single tier instead of being scattered throughout an application. Another possible reason might be the emergence of clear leaders in the DBMS market over the last decade, such that managers perceive less risk in which database engine they choose.
If you were to peruse the various writings on the relational model, you would come across terminology that you will not find used in this book (such as relations and tuples). Instead, we use practical terms such as tables and rows, and we refer to the various parts of a SQL statement by name rather than by function (i.e., "SELECT clause" instead of projection). With all due respect to Dr. Codd, you will never hear the word tuple used in a business setting, and, since this book is targeted toward people who use Oracle products to solve business problems, you won't find it here either.