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SQL 结构式查询语言 结构式查询语言 /S Q L/ An industry-standard
language for creating, updating and, querying {relational
database management systems}.
SQL was developed by {IBM} in the 1970s for use in {System R}.
It is the {de facto standard} as well as being an {ISO} and
{ANSI} {standard}. It is often embedded in general purpose
programming languages.
The first SQL standard, in 1986, provided basic language
constructs for defining and manipulating {tables} of data; a
revision in 1989 added language extensions for {referential
integrity} and generalised {integrity} {constraints}. Another
revision in 1992 provided facilities for {schema} manipulation
and {data administration}, as well as substantial enhancements
for data definition and data manipulation.
Development is currently underway to enhance SQL into a
computationally complete language for the definition and
management of {persistent}, complex objects. This includes:
generalisation and specialisation hierarchies, {multiple
inheritance}, user defined {data types}, {triggers} and
{assertions}, support for {knowledge based systems},
{recursive query expressions}, and additional data
administration tools. It also includes the specification of
{abstract data types} (ADTs), object identifiers, {methods},
{inheritance}, {polymorphism}, {encapsulation}, and all of the
other facilities normally associated with object data
management.
The emerging {SQL3} standard is expected to be complete in
1998.
According to Allen G. Taylor, SQL does __not__ stand for
"Structured Query Language". That, like "SEQUEL" (and its
pronunciation /see'kw*l/), was just another unofficial name
for a precursor of SQL. However, the IBM SQL Reference manual
for DB2 and Craig Mullins's "DB2 Developer's Guide" say SQL
__does__ stand for "Structured Query Language".
{SQL Standards (http://jcc.com/sql_stnd.html)}.
{An SQL parser
(ftp://ftp.ora.com/published/oreilly/nutshell/lexyacc/)} is
described in "Lex & Yacc", by Levine, Mason & Brown published
by O'Reilly.
{The 1995 SQL Reunion: People, Projects, and Politics
(http://mcjones.org/System_R/SQL_Reunion_95/)}.
["A Guide to the SQL Standard", C.J. Date, A-W 1987].
["SQL for Dummies", Allen G. Taylor, IDG Books Worldwide].
(2005-11-17)
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