Oracle SQL: the Essential Reference

The Origins of SQL

So, where did SQL come from, how has it evolved, and where is it going? The story of SQL begins at the IBM research laboratories near San Jose, California in the 1970s. Ted Codd, a mathematician and research fellow at IBM, created a formal theory of data management and wrote a seminal paper entitled "A Relational Model of Data for Large Shared Data Banks", published in the Communications of the ACM in June 1970. He defined the relational data model, consisting of data structures (tables of rows and columns); operations (like selection, projection, and joins) on that data; and integrity rules that ensure consistency of data (primary keys and referential integrity, for example).

Codd's rigorous mathematical definition of the relational model allowed him to define a procedure for designing databases that preserve data integrity and minimize redundancy. So-called normalization theory defines third normal form, where every table in the database has a primary key that can uniquely identify each row in the table, and where each column in the row is dependent on the primary key. A database designed in third normal form is especially able to support applications and queries that cannot be anticipated at database design time.

Codd also defined a mathematical data manipulation language, DSL/Alpha. This language was based on the mathematics of set theory, and could be used to express queries and manipulate the data tables that comprise a relational database. Codd proved ...