The SQL language is subdivided into several language elements, including: Clauses, which are constituent components of statements and queries. (In some cases, these. Cheat Sheets for Developers. The largest collection of reference cards for developers. InformationWeek.com: News, analysis and research for business technology professionals, plus peer-to-peer knowledge sharing. Engage with our community. Microsoft Access Tools For Databases Demystified QuizSQL - Wikipedia. SQL ( ( listen)ESS- kew- EL[4] or ( listen)SEE- kwəl,[5]Structured Query Language[6][7][8][9]) is a domain- specific language used in programming and designed for managing data held in a relational database management system (RDBMS), or for stream processing in a relational data stream management system (RDSMS). In comparison to older read/write APIs like ISAM or VSAM, SQL offers two main advantages: First, it introduced the concept of accessing many records with one single command, and second, it eliminates the need to specify how to reach a record, e. Originally based upon relational algebra and tuple relational calculus, SQL consists of a data definition language, data manipulation language, and data control language. The scope of SQL includes data insert, query, update and delete, schema creation and modification, and data access control. Although SQL is often described as, and to a great extent is, a declarative language (4. GL), it also includes procedural elements. SQL was one of the first commercial languages for Edgar F. Codd's relational model, as described in his influential 1. A Relational Model of Data for Large Shared Data Banks".[1. Despite not entirely adhering to the relational model as described by Codd, it became the most widely used database language.[1.SQL became a standard of the American National Standards Institute (ANSI) in 1. Ms Office 2003 Dk Sp1 Isopure there. International Organization for Standardization (ISO) in 1.Since then, the standard has been revised to include a larger set of features.Despite the existence of such standards, most SQL code is not completely portable among different database systems without adjustments. History[edit]SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce in the early 1. 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 1. The acronym SEQUEL was later changed to SQL because "SEQUEL" was a trademark of the UK- based. Hawker Siddeley aircraft company.[1. In the late 1. 97. Relational Software, Inc. 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 1. 97. 9, Relational Software, Inc. SQL, Oracle V2 (Version. VAX computers. After testing SQL at customer test sites to determine the usefulness and practicality of the system, IBM began developing commercial products based on their System R prototype including System/3. SQL/DS, and DB2, which were commercially available in 1. SQL deviates in several ways from its theoretical foundation, the relational model and its tuple calculus. In that model, a table is a set of tuples, while in SQL, tables and query results are lists of rows: the same row may occur multiple times, and the order of rows can be employed in queries (e. LIMIT clause). Critics argue that SQL should be replaced with a language that strictly returns to the original foundation: for example, see The Third Manifesto. A chart showing several of the SQL language elements that compose a single statement. 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.)[1. 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 (3. VL) (true/false/unknown) or Booleantruth 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. SQL statements also include the semicolon ("; ") statement terminator. 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. Procedural extensions[edit]SQL is designed for a specific purpose: to query data contained in a relational database. SQL is a set- based, declarative programming language, not an imperative programming language like C or BASIC. However, extensions to Standard SQL add procedural programming language functionality, such as control- of- flow constructs. These include: In addition to the standard SQL/PSM extensions and proprietary SQL extensions, procedural and object- oriented programmability is available on many SQL platforms via DBMS integration with other languages. The SQL standard defines SQL/JRT extensions (SQL Routines and Types for the Java Programming Language) to support Java code in SQL databases. SQL Server 2. 00. SQLCLR (SQL Server Common Language Runtime) to host managed . NET assemblies in the database, while prior versions of SQL Server were restricted to unmanaged extended stored procedures primarily written in C. Postgre. SQL lets users write functions in a wide variety of languages—including Perl, Python, Tcl, Java. Script (PL/V8) and C.[1. Interoperability and standardization[edit]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. Particular exceptions are Postgre. SQL[2. 0] and Mimer SQL[2. Popular implementations of SQL commonly omit support for basic features of Standard SQL, such as the DATE or TIME data types. The most obvious such examples, and incidentally the most popular commercial and proprietary SQL DBMSs, are Oracle (whose DATE behaves as DATETIME,[2. TIME type)[2. 4] and MS SQL Server (before the 2. As a result, SQL code can rarely be ported between database systems without modifications. There are several reasons for this lack of portability between database systems: The complexity and size of the SQL standard means that most implementors do not support the entire standard. The standard does not specify database behavior in several important areas (e. 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. Many database vendors have large existing customer bases; where the newer version of the SQL standard conflicts with the prior behavior of the vendor's database, the vendor may be unwilling to break backward compatibility. There is little commercial incentive for vendors to make it easier for users to change database suppliers (see vendor lock- in). Users evaluating database software tend to place other factors such as performance higher in their priorities than standards conformance. SQL was adopted as a standard by the American National Standards Institute (ANSI) in 1. SQL- 8. 6[2. 5] and the International Organization for Standardization (ISO) in 1. It is maintained by ISO/IEC JTC 1, Information technology, Subcommittee SC 3. Data management and interchange. The standard is commonly denoted by the pattern: ISO/IEC 9. Part n: title, or, as a shortcut, ISO/IEC 9. ISO/IEC 9. 07. 5 is complemented by ISO/IEC 1. SQL Multimedia and Application Packages (SQL/MM), which defines SQL based interfaces and packages to widely spread applications like video, audio and spatial data. Until 1. 99. 6, the National Institute of Standards and Technology (NIST) data management standards program certified SQL DBMS compliance with the SQL standard. Vendors now self- certify the compliance of their products.[2. The original standard declared that the official pronunciation for "SQL" was an initialism: ("es queue el").[1. Regardless, many English- speaking database professionals (including Donald Chamberlin himself[5]) use the acronym- like pronunciation of ("sequel"),[2. SEQUEL".[1. 4][1. The SQL standard has gone through a number of revisions: Year. Name. Alias. Comments. SQL- 8. 6SQL- 8. 7First formalized by ANSI. SQL- 8. 9FIPS 1. 27- 1. Minor revision that added integrity constraints, adopted as FIPS 1. SQL- 9. 2SQL2, FIPS 1.
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