Importance of SQL

SQL is the first and, so far, only standard database language to gain wide acceptance. The
only other standard database language, the Network Database Language (NDL), based on
the CODASYL network model, has few followers. Nearly every major current vendor provides
database products based on SQL or with an SQL interface, and most are represented
on at least one of the standard-making bodies. There is a huge investment in the SQL language
both by vendors and by users. It has become part of application architectures such
as IBM’s Systems Application Architecture (SAA) and is the strategic choice of many
large and influential organizations, for example, the X/OPEN consortium for UNIX standards.
SQL has also become a Federal Information Processing Standard (FIPS), to which
conformance is required for all sales of DBMSs to the US government. The SQL Access
Group, a consortium of vendors, defined a set of enhancements to SQL that would support
interoperability across disparate systems.
SQL is used in other standards and even influences the development of other standards
as a definitional tool. Examples include ISO’s Information Resource Dictionary System
(IRDS) standard and Remote Data Access (RDA) standard. The development of the
language is supported by considerable academic interest, providing both a theoretical basis
for the language and the techniques needed to implement it successfully. This is especially
true in query optimization, distribution of data, and security. There are now specialized
implementations of SQL that are directed at new markets, such as OnLine Analytical
Processing (OLAP).
Terminology
The ISO SQL standard does not use the formal terms of relations, attributes, and tuples,
instead using the terms tables, columns, and rows. In our presentation of SQL we mostly
use the ISO terminology. It should also be noted that SQL does not adhere strictly to the
definition of the relational model described in Chapter 3. For example, SQL allows the
table produced as the result of the SELECT statement to contain duplicate rows, it imposes
an ordering on the columns, and it allows the user to order the rows of a result table.