The Probert Encyclopaedia of Science & Technology

SQL

SQL stands for Structured Query Language. Often referred to as Sequel for short,
SQL was developed as a query language to access mainframe databases such as IBM's DB2. PC products that incorporate
SQL are IBM's OS/2 Extended Edition, dBASE IV, SQL Server from Ashton-Tate and Microsoft, Paradox, DataEASE (using a modified form called DQL), PC/FOCUS, and many others. PC implementations of SQL fall into, two categories. Firstly, SQL commands can be written directly by programmers and experienced users to access databases. The second implementation recognises that most PC users are not programmers and do not want to learn SQL and so provides them with their normal friendly user interface. The underlying software then writes the SQL commands directly for them, which are used to query SQL server databases. Another benefit of SQL is that it will provide a common programming language for different machine architectures, i.e. code written on an IBM mainframe can be moved to a PC with less rewriting than with conventional languages. A full implementation of SQL also contains a very critical component for creating robust transactional databases. Often referred to as ROLL RACK/COMMIT, the facility allows a transaction that was interrupted half
way through updating multiple files to be rolled back, thereby preventing damage to the data files. Many PC implementations of SQL are subsets of the ANSI standard, and some include extensions to the ANS standard.
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