| /ˌɛsˌkjuˈɛl/ S-Q-L; or alternatively as "sequel") is a domain-specific language used to manage data, especially in a relational database management system (RDBMS). It is particularly useful in handling structured data, i.e., data incorporating relations among entities and variables.
Introduced in the 1970s, SQL offered two main advantages over older read–write APIs such as ISAM or VSAM. Firstly, it introduced the concept of accessing many records with one single command. Secondly, it eliminates the need to specify how to reach a record, i.e., with or without an index.
Originally based upon relational algebra and tuple relational calculus, SQL consists of many types of statements, which may be informally classed as sublanguages, commonly: data query language (DQL), data definition language (DDL), data control language (DCL), and data manipulation language (DML).
The scope of SQL includes data query, data manipulation (insert, update, and delete), data definition (schema creation and modification), and data access control. Although SQL is essentially a declarative language (4GL), it also includes procedural elements.
SQL was one of the first commercial languages to use Edgar F. Codd's relational model. The model was described in his influential 1970 paper, "A Relational Model of Data for Large Shared Data Banks". Despite not entirely adhering to the relational model as described by Codd, SQL became the most widely used database language.
SQL became a standard of the American National Standards Institute (ANSI) in 1986 and of the International Organization for Standardization (ISO) in 1987. Since then, the standard has been revised multiple times to include a larger set of features and incorporate common extensions. Despite the existence of standards, virtually no implementations in existence adhere to it fully, and most SQL code requires at least some changes before being ported to different database systems.
SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce after learning about the relational model from Edgar F. Codd in the early 1970s. This version, initially called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM's original quasirelational database management system, System R, which a group at IBM San Jose Research Laboratory had developed during the 1970s.
Chamberlin and Boyce's first attempt at a relational database language was SQUARE (Specifying Queries in A Relational Environment), but it was difficult to use due to subscript/superscript notation. After moving to the San Jose Research Laboratory in 1973, they began work on a sequel to SQUARE. The original name SEQUEL, which is widely regarded as a pun on QUEL, the query language of Ingres, was later changed to SQL (dropping the vowels) because "SEQUEL" was a trademark of the UK-based Hawker Siddeley Dynamics Engineering Limited company. The label SQL later became the acronym for Structured Query Language.
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/38, SQL/DS, and IBM Db2, which were commercially available in 1979, 1981, and 1983, respectively. IBM's endorsement caused the industry to move to SQL from alternatives like QUEL.
In the late 1970s, Relational Software, Inc. (now 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 1979, Relational Software introduced one of the first commercially available implementations of SQL, Oracle V2 (Version2) for VAX computers.
By 1986, ANSI and ISO standard groups officially adopted the standard "Database Language SQL" language definition. New versions of the standard were published in 1989, 1992, 1996, 1999, 2003, 2006, 2008, 2011, 2016 and, most recently, 2023.
Interoperability and standardizationedit| SQL language revisions |
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| /ˌɛsˌkjuːˈɛl/ ("ess cue el"). Regardless, many English-speaking database professionals (including Donald Chamberlin himself) use the acronym-like pronunciation of 𝚄𝙿𝙳𝙰𝚃𝙴 𝚌𝚕𝚊𝚞𝚜𝚎:{𝚄𝙿𝙳𝙰𝚃𝙴 𝚌𝚘𝚞𝚗𝚝𝚛𝚒𝚎𝚜⏞𝚝𝚊𝚋𝚕𝚎}𝚂𝙴𝚃 𝚌𝚕𝚊𝚞𝚜𝚎:{𝚂𝙴𝚃 𝚙𝚘𝚙𝚞𝚕𝚊𝚝𝚒𝚘𝚗⏞𝚌𝚘𝚕𝚞𝚖𝚗= 𝚙𝚘𝚙𝚞𝚕𝚊𝚝𝚒𝚘𝚗+𝟷⏟𝚕𝚒𝚝𝚎𝚛𝚊𝚕⏞𝚎𝚡𝚙𝚛𝚎𝚜𝚜𝚒𝚘𝚗}𝚆𝙷𝙴𝚁𝙴 𝚌𝚕𝚊𝚞𝚜𝚎:{𝚆𝙷𝙴𝚁𝙴 𝚗𝚊𝚖𝚎⏞𝚌𝚘𝚕𝚞𝚖𝚗='𝚄𝚂𝙰′⏞𝚕𝚒𝚝𝚎𝚛𝚊𝚕⏞𝚎𝚡𝚙𝚛𝚎𝚜𝚜𝚒𝚘𝚗⏟𝚙𝚛𝚎𝚍𝚒𝚌𝚊𝚝𝚎};}𝚜𝚝𝚊𝚝𝚎𝚖𝚎𝚗𝚝⏟𝚂𝚀𝙻 𝚚𝚞𝚎𝚛𝚢 A chart showing several of the SQL language elements comprising 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.)
- 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 (3VL) (true/false/unknown) or 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.
- 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 extensionseditSQL 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.
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. Microsoft SQL Server 2005 uses the 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. PostgreSQL lets users write functions in a wide variety of languages—including Perl, Python, Tcl, JavaScript (PL/V8) and C.
A distinction should be made between alternatives to SQL as a language, and alternatives to the relational model itself. Below are proposed relational alternatives to the SQL language. See navigational database and NoSQL for alternatives to the relational model.
\n* [[HTSQL]]: URL based query method\n* [[IBM Business System 12]] (IBM BS12): one of the first fully relational database management systems, introduced in 1982\n* [[ISBL]]\n* [[Java Object Oriented Querying|jOOQ]]: SQL implemented in Java as an [[Domain-specific language|internal domain-specific language]]\n* [[Java Persistence Query Language]] (JPQL): The query language used by the Java Persistence API and [[Hibernate (Java)|Hibernate]] persistence library\n* [[JavaScript]]: [[MongoDB]] implements its query language in a JavaScript API.\n* [[Language Integrated Query|LINQ]]: Runs SQL statements written like language constructs to query collections directly from inside [[.NET Framework|.Net]] code\n* [[Object Query Language]]\n* QBE ([[Query By Example]]) created by Moshè Zloof, IBM 1977\n* [[QUEL query languages|QUEL]] introduced in 1974 by the U.C. Berkeley Ingres project, closer to [[tuple relational calculus]] than SQL\n* [[XQuery]]\n",{"template":{"target":{"wt":"Div col end","href":"./Template:Div_col_end"},"params":{},"i":1}}]}'>
Distributed SQL processingeditDistributed Relational Database Architecture (DRDA) was designed by a workgroup within IBM from 1988 to 1994. DRDA enables network-connected relational databases to cooperate to fulfill SQL requests.
An interactive user or program can issue SQL statements to a local RDB and receive tables of data and status indicators in reply from remote RDBs. SQL statements can also be compiled and stored in remote RDBs as packages and then invoked by package name. This is important for the efficient operation of application programs that issue complex, high-frequency queries. It is especially important when the tables to be accessed are located in remote systems.
The messages, protocols, and structural components of DRDA are defined by the Distributed Data Management Architecture. Distributed SQL processing ala DRDA is distinctive from contemporary distributed SQL databases.
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.g., in the LIMIT clause).
Critics argue that SQL should be replaced with a language that returns strictly to the original foundation: for example, see The Third Manifesto by Hugh Darwen and C.J. Date (2006, ISBN 0-321-39942-0).
Orthogonality and completenesseditEarly specifications did not support major features, such as primary keys. Result sets could not be named, and subqueries had not been defined. These were added in 1992.
The lack of sum types has been described as a roadblock to full use of SQL's user-defined types. JSON support, for example, needed to be added by a new standard in 2016.
The concept of
{{cite web | last = Paul | first = Ryan | title = A guided tour of the Microsoft Command Shell | url = https://arstechnica.com/information-technology/2005/10/msh/ | website = Ars Technica | date = 24 October 2005 | access-date = 10 April 2011 }}</ref>\n<ref name=\"iana\">{{cite web | url = https://www.iana.org/assignments/media-types/application/sql | title = Media Type registration for application/sql | publisher = [[Internet Assigned Numbers Authority]] | date = 10 April 2013 | access-date = 10 April 2013 | archive-date = 7 May 2013 | archive-url = https://web.archive.org/web/20130507140101/http://www.iana.org/assignments/media-types/application/sql | url-status = live }}</ref>\n<ref name=\"application/sql\">{{cite web | url = http://tools.ietf.org/html/rfc6922 | title = The application/sql Media Type, RFC 6922 | page = 3 | publisher = [[Internet Engineering Task Force]] | date = April 2013 | doi = 10.17487/RFC6922 | access-date = 10 April 2013 | last1 = Shafranovich | first1 = Y. | archive-date = 13 October 2014 | archive-url = https://web.archive.org/web/20141013172428/http://tools.ietf.org/html/rfc6922 | url-status = live }}</ref>\n<ref name=\"learningSQL\">{{ cite book | last = Beaulieu | first = Alan | title = Learning SQL | editor = Mary E Treseler | publisher = O'Reilly | location = Sebastopol, CA, USA | date = April 2009 | edition = 2nd | isbn = 978-0-596-52083-0 }}</ref>\n\n<ref name=\"codd-relational-model\">{{ cite journal | last = Codd | first = Edgar F. | title = A Relational Model of Data for Large Shared Data Banks | journal = Communications of the ACM | volume = 13 | issue = 6 | pages = 377–87 | date = June 1970 | doi = 10.1145/362384.362685 | s2cid = 207549016 }}</ref>\n<ref name=\"SQL-Fundamentals\">{{cite news | last = Chapple | first = Mike | title = SQL Fundamentals | work = Databases | publisher = About.com | url = http://databases.about.com/od/sql/a/sqlfundamentals.htm | access-date = 28 January 2009 | archive-date = 22 February 2009 | archive-url = https://web.archive.org/web/20090222225300/http://databases.about.com/od/sql/a/sqlfundamentals.htm }}</ref>\n<ref name=\"IBM-sql\">{{cite web | title = Structured Query Language (SQL) | publisher = International Business Machines | url = http://publib.boulder.ibm.com/infocenter/db2luw/v9/index.jsp?topic=com.ibm.db2.udb.admin.doc/doc/c0004100.htm | date = 27 October 2006 | access-date = 10 June 2007 }}</ref>\n<ref name=\"ISO 9075:1987\">{{cite web | url = https://www.iso.org/standard/76583.html | title = ISO 9075:1987: Information technology – Database languages – SQL – Part 1: Framework (SQL/Framework) | date = 1 June 2023 | access-date = 24 June 2025 }}</ref>\n<ref name=\"chamberlin-boyce-sequel\">{{ cite journal | last1 = Chamberlin | first1 = Donald D | last2 = Boyce | first2 = Raymond F | title = SEQUEL: A Structured English Query Language | journal = Proceedings of the 1974 ACM SIGFIDET Workshop on Data Description, Access and Control | pages = 249–64 | publisher = Association for Computing Machinery | year = 1974 | url = http://www.almaden.ibm.com/cs/people/chamberlin/sequel-1974.pdf | access-date = 9 June 2007 | archive-url=https://web.archive.org/web/20070926212100/http://www.almaden.ibm.com/cs/people/chamberlin/sequel-1974.pdf |archive-date=26 September 2007 }}</ref>\n<ref name=\"oppel-databases\">{{cite book | last = Oppel | first = Andy | title = Databases Demystified | publisher = McGraw-Hill Osborne Media | date = 27 February 2004 | location = [[San Francisco, CA]] | pages = 90–1 | url = http://www.mhprofessional.com/product.php?cat=112&isbn=0071469605 | isbn = 978-0-07-146960-9 | archive-date = 14 January 2012 | access-date = 12 May 2011 | archive-url = https://web.archive.org/web/20120114180544/http://www.mhprofessional.com/product.php?cat=112&isbn=0071469605 | url-status = live }}</ref>\n<ref name=\"IBM-history\">{{cite web | title = History of IBM, 1978 | work = IBM Archives | date = 23 January 2003 | publisher = IBM | url = http://www-03.ibm.com/ibm/history/history/year_1978.html | archive-url = https://web.archive.org/web/20050117192541/http://www-03.ibm.com/ibm/history/history/year_1978.html | archive-date = 17 January 2005 | access-date = 9 June 2007 }}</ref>\n<ref name=\"ANSI/ISO/IEC\">ANSI/ISO/IEC International Standard (IS). Database Language SQL—Part 2: Foundation (SQL/Foundation). 1999.</ref>\n<ref name=\"PostgreSQL server programming\">{{cite web | title = PostgreSQL server programming | work = PostgreSQL 9.1 official documentation | publisher = postgresql.org | year = 2011 | url = http://www.postgresql.org/docs/9.1/static/server-programming.html | access-date = 9 March 2012 | archive-date = 2 March 2012 | archive-url = https://web.archive.org/web/20120302074948/http://www.postgresql.org/docs/9.1/static/server-programming.html | url-status = live }}</ref>\n<ref name=\"PROLE\">{{cite web |url=http://lbd.udc.es/jornadas2011/actas/PROLE/PROLE/S5/13_article.pdf |title=Outer Joins in a Deductive Database System |author=Fernando Saenz-Perez |website=Lbd.udc.es |access-date=16 January 2017 |archive-date=9 August 2016 |archive-url=https://web.archive.org/web/20160809225439/http://lbd.udc.es/jornadas2011/actas/PROLE/PROLE/S5/13_article.pdf |url-status=live }}</ref>\n<ref name=\"About PostgreSQL\">{{cite web | title = About PostgreSQL | work = PostgreSQL 9.1 official website | publisher = PostgreSQL Global Development Group | year = 2012 | url = http://www.postgresql.org/about/ | quote = PostgreSQL prides itself in standards compliance. Its SQL implementation strongly conforms to the ANSI-SQL:2008 standard | access-date = 9 March 2012 | archive-date = 9 March 2012 | archive-url = https://web.archive.org/web/20120309174528/http://www.postgresql.org/about/ | url-status = live }}</ref>\n<ref name=\"Mimer SQL, Built on Standards\">{{cite web | title = Mimer SQL, Built on Standards | work = Mimer SQL official website | publisher = Mimer Information Technology | year = 2009 | url = http://developer.mimer.com/features/feature_6.htm | access-date = 11 December 2018 | archive-date = 3 May 2016 | archive-url = https://web.archive.org/web/20160503020216/http://developer.mimer.com/features/feature_6.htm | url-status = live }}</ref>\n<ref name=\"Ora DATE\">{{cite book | first1 = Diana | last1 = Lorentz | first2 = Mary Beth | last2 = Roeser | first3 = Sundeep | last3 = Abraham | first4 = Angela | last4 = Amor | first5 = Geeta | last5 = Arora | first6 = Vikas | last6 = Arora | first7 = Lance | last7 = Ashdown | first8 = Hermann | last8 = Baer | first9 = Shrikanth | last9 = Bellamkonda | series = Oracle Database Documentation Library | publisher = Oracle USA, Inc | place = Redwood City, CA | title = Oracle Database SQL Language Reference 11g Release 2 (11.2) | chapter = Basic Elements of Oracle SQL: Data Types | orig-date = 1996 | date = October 2010 | access-date = 29 December 2010 | chapter-url = http://download.oracle.com/docs/cd/E11882_01/server.112/e17118/sql_elements001.htm#sthref154 | quote = For each <code>DATE</code> value, Oracle stores the following information: century, year, month, date, hour, minute, and second | archive-date = 20 November 2010 | archive-url = https://web.archive.org/web/20101120055711/http://download.oracle.com/docs/cd/E11882_01/server.112/e17118/sql_elements001.htm#sthref154 | url-status = live }}</ref>\n<ref name=\"Ora DATETIME\">{{cite book | first1 = Diana | last1 = Lorentz | first2 = Mary Beth | last2 = Roeser | first3 = Sundeep | last3 = Abraham | first4 = Angela | last4 = Amor | first5 = Geeta | last5 = Arora | first6 = Vikas | last6 = Arora | first7 = Lance | last7 = Ashdown | first8 = Hermann | last8 = Baer | first9 = Shrikanth | last9 = Bellamkonda | series = Oracle Database Documentation Library | publisher = Oracle USA, Inc | place = Redwood City, CA | title = Oracle Database SQL Language Reference 11g Release 2 (11.2) | chapter = Basic Elements of Oracle SQL: Data Types | orig-date = 1996 | date = October 2010 | access-date = 29 December 2010 | chapter-url = http://download.oracle.com/docs/cd/E11882_01/server.112/e17118/sql_elements001.htm#sthref154 | quote = The datetime data types are <code>DATE</code>... | archive-date = 20 November 2010 | archive-url = https://web.archive.org/web/20101120055711/http://download.oracle.com/docs/cd/E11882_01/server.112/e17118/sql_elements001.htm#sthref154 | url-status = live }}</ref>\n<ref name=\"Ora TIME\">{{cite book | first1 = Diana | last1 = Lorentz | first2 = Mary Beth | last2 = Roeser | first3 = Sundeep | last3 = Abraham | first4 = Angela | last4 = Amor | first5 = Geeta | last5 = Arora | first6 = Vikas | last6 = Arora | first7 = Lance | last7 = Ashdown | first8 = Hermann | last8 = Baer | first9 = Shrikanth | last9 = Bellamkonda | series = Oracle Database Documentation Library | publisher = Oracle USA, Inc | place = Redwood City, CA | title = Oracle Database SQL Language Reference 11g Release 2 (11.2) | chapter = Basic Elements of Oracle SQL: Data Types | orig-date = 1996 | date = October 2010 | access-date = 29 December 2010 | chapter-url = http://download.oracle.com/docs/cd/E11882_01/server.112/e17118/sql_elements001.htm#i54335 | quote = Do not define columns with the following SQL/DS and DB2 data types, because they have no corresponding Oracle data type:... <code>TIME</code> | archive-date = 20 November 2010 | archive-url = https://web.archive.org/web/20101120055711/http://download.oracle.com/docs/cd/E11882_01/server.112/e17118/sql_elements001.htm#i54335 | url-status = live }}</ref>\n<ref name=\"X3H2\">{{cite book | chapter-url = http://special.lib.umn.edu/findaid/xml/cbi00168.xml | publisher = American National Standards Institute | title = X3H2 Records, 1978–95 | chapter = Finding Aid | archive-date = 19 June 2010 | access-date = 26 April 2008 | archive-url = https://web.archive.org/web/20100619143221/http://special.lib.umn.edu/findaid/xml/cbi00168.xml | url-status = live }}</ref>\n<ref name=\"Doll\">{{cite web | last = Doll | first = Shelley | title = Is SQL a Standard Anymore? | work = TechRepublic's Builder.com | publisher = TechRepublic | date = 19 June 2002 | url = http://articles.techrepublic.com.com/5100-10878_11-1046268.html | access-date = 12 April 2016 | archive-url = https://web.archive.org/web/20120705163024/http://www.techrepublic.com/article/is-sql-a-standard-anymore/1046268 | archive-date = 5 July 2012 }}</ref>\n<ref name=\"Gillespie\">{{cite web | last = Gillespie | first = Patrick | url = http://patorjk.com/blog/2012/01/26/pronouncing-sql-s-q-l-or-sequel/ | title = Pronouncing SQL: S-Q-L or Sequel? | access-date = 12 February 2012 | archive-date = 27 May 2012 | archive-url = https://web.archive.org/web/20120527131959/http://patorjk.com/blog/2012/01/26/pronouncing-sql-s-q-l-or-sequel/ | url-status = live }}</ref>\n<ref name=\"Melton\">{{cite book | title = Understanding the New SQL: A Complete Guide | last = Melton | first = Jim | author2 = Alan R Simon | year = 1993 | publisher = Morgan Kaufmann | isbn = 978-1-55860-245-8 | page = [https://archive.org/details/understandingnew00melt/page/536 536] | chapter = 1.2. What is SQL? | quote = SQL (correctly pronounced \"ess cue ell,\" instead of the somewhat common \"sequel\")... | chapter-url-access = registration | chapter-url = https://archive.org/details/understandingnew00melt | url = https://archive.org/details/understandingnew00melt/page/536 }}</ref>\n<ref name=\"SQLXML2006\">{{ cite book | title = SQL/XML:2006 - Evaluierung der Standardkonformität ausgewählter Datenbanksysteme | last = Wagner | first = Michael | year = 2010 | publisher = Diplomica Verlag | isbn = 978-3-8366-9609-8 | page = 100 }}</ref>\n<ref name=\"iablog.sybase.com-paulley\">{{ cite web |date=July 2008 |title=SQL:2008 now an approved ISO international standard |publisher=Sybase |url=http://iablog.sybase.com/paulley/2008/07/sql2008-now-an-approved-iso-international-standard/ |archive-url=https://web.archive.org/web/20110628130925/http://iablog.sybase.com/paulley/2008/07/sql2008-now-an-approved-iso-international-standard/ |archive-date=28 June 2011 }}</ref>\n<ref name=\"Andrew\">{{citation | url = http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt | format = text | title = SQL:1992 draft | access-date = 8 October 2009 | archive-date = 21 June 2006 | archive-url = https://web.archive.org/web/20060621035823/http://www.contrib.andrew.cmu.edu/%7Eshadow/sql/sql1992.txt | url-status = live }}</ref>\n<ref name=\"Whitemarsh2\">{{ citation | url = https://www.wiscorp.com/sql20nn.zip | format = Zip | title = SQL:2011 draft | publisher = Whitemarsh Information Systems Corporation | archive-url = https://web.archive.org/web/20230525220603/https://www.wiscorp.com/sql20nn.zip | archive-date = 25 May 2023 }}</ref>\n<ref name=\"features_2011\">{{ cite web | title = What's new in SQL:2011 | url = https://sigmodrecord.org/publications/sigmodRecord/1203/pdfs/10.industry.zemke.pdf | author = Fred Zemke |publisher=Oracle Corporation | year = 2012 }}</ref>\n\n<ref name=\"feature_temporal\">{{ cite journal | title = Temporal features in SQL:2011 | url = http://cs.ulb.ac.be/public/_media/teaching/infoh415/tempfeaturessql2011.pdf | author = Krishna Kulkarni, Jan-Eike Michels |journal=SIGMOD Record | date = September 2012 |volume=41 |number=3 }}</ref>"}},"i":0}}]}'>
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