Structured Query Language, or simple SQL is a programming language designed for managing data in relational database management systems (RDBMS). Its scope includes data insert, query, update and delete, schema creation and modification, and data access control.
SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce in the early 1970s. This version, initially called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM’s original quasi-relational database management system, System R, which a group at IBM San Jose Research Laboratory had developed during the 1970s. The acronym SEQUEL was later changed to SQL because “SEQUEL” was a trademark of the UK-based Hawker Siddeley aircraft company.
The first Relational Database Management System (RDBMS) was RDMS, developed at MIT in the early 1970s, soon followed by Ingres, developed in 1974 at U.C. Berkeley. Ingres implemented a query language known as QUEL, which was later supplanted in the marketplace by SQL.
In the late 1970s, Relational Software, Inc. (now Oracle Corporation) saw the potential of the concepts described by Codd, Chamberlin, and Boyce and developed their own SQL-based RDBMS with aspirations of selling it to the U.S. Navy, Central Intelligence Agency, and other U.S. government agencies. In June 1979, Relational Software, Inc. introduced the first commercially available implementation of SQL, Oracle V2 (Version2) for VAX computers. Oracle V2 beat IBM’s August release of the System/38 RDBMS to market by a few weeks.
The SQL language is subdivided into several language elements, including:
- Clauses, which are constituent components of statements and queries. (In some cases, these are optional);
- Expressions, which can produce either scalar values or tables consisting of columns and rows of data;
- Predicates, which specify conditions that can be evaluated to SQL three-valued logic (3VL) or Boolean (true/false/unknown) truth values and which are used to limit the effects of statements and queries, or to change program flow;
- Queries, which retrieve the data based on specific criteria. This is the most important element of SQL;
- Statements, which may have a persistent effect on schemata and data, or which may control transactions, program flow, connections, sessions, or diagnostics.
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