This article is about the database language. For the topic of the word, see sequel. SQL was one of the first commercial languages for Edgar F. Codd’s relational model, as described in his influential 1970 paper, “A Relational Model of Data for Ansi n14 5 pdf Shared Data Banks”.
SQL was initially developed at IBM by Donald D. Boyce after learning about the relational model from Ted Codd in the early 1970s. Chamberlin and Boyce’s first attempt of a relational database language was Square, but it was difficult to use due to subscript notation. After moving to the San Jose Research Laboratory in 1973, they began work on SEQUEL.
In the late 1970s, Relational Software, Inc. Codd, Chamberlin, and Boyce, and developed their own SQL-based RDBMS with aspirations of selling it to the U. DS, and DB2, which were commercially available in 1979, 1981, and 1983, respectively. SQL deviates in several ways from its theoretical foundation, the relational model and its tuple calculus.
Critics argue that SQL should be replaced with a language that strictly returns to the original foundation: for example, see The Third Manifesto. Clauses, which are constituent components of statements and queries. In some cases, these are optional. Boolean truth values and 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 an important element of SQL. Statements, which may have a persistent effect on schemata and data, or may control transactions, program flow, connections, sessions, or diagnostics.
Though not required on every platform, it is defined as a standard part of the SQL grammar. Insignificant whitespace is generally ignored in SQL statements and queries, making it easier to format SQL code for readability. SQL is designed for a specific purpose: to query data contained in a relational database. PSM extensions and proprietary SQL extensions, procedural and object-oriented programmability is available on many SQL platforms via DBMS integration with other languages. SQL implementations are incompatible between vendors and do not necessarily completely follow standards.
In particular date and time syntax, string concatenation, NULLs, and comparison case sensitivity vary from vendor to vendor. Popular implementations of SQL commonly omit support for basic features of Standard SQL, such as the DATE or TIME data types. The complexity and size of the SQL standard means that most implementors do not support the entire standard. The SQL standard precisely specifies the syntax that a conforming database system must implement.
However, the standard’s specification of the semantics of language constructs is less well-defined, leading to ambiguity. SQL standard conflicts with the prior behavior of the vendor’s database, the vendor may be unwilling to break backward compatibility. Users evaluating database software tend to place other factors such as performance higher in their priorities than standards conformance. SQL based interfaces and packages to widely spread applications like video, audio and spatial data. SQL DBMS compliance with the SQL standard. Vendors now self-certify the compliance of their products. Minor revision that added integrity constraints, adopted as FIPS 127-1.
Entry Level SQL-92 adopted as FIPS 127-2. IEC 9075-14:2006 defines ways that SQL can be used with XML. It defines ways of importing and storing XML data in an SQL database, manipulating it within the database, and publishing both XML and conventional SQL-data in XML form. Legalizes ORDER BY outside cursor definitions. Adds INSTEAD OF triggers, TRUNCATE statement, FETCH clause.
Enhancements for window functions and FETCH clause. Adds row pattern matching, polymorphic table functions, JSON. Interested parties may purchase SQL standards documents from ISO, IEC or ANSI. A draft of SQL:2008 is freely available as a zip archive. The SQL standard is divided into nine parts. It contains the most central elements of the language and consists of both mandatory and optional features. It standardizes procedural extensions for SQL, including flow of control, condition handling, statement condition signals and resignals, cursors and local variables, and assignment of expressions to variables and parameters.