SQL

SQL (/ˌɛsˌkjuːˈɛl/ (listen) S-Q-L,[4] /ˈsiːkwəl/ "sequel"; Structured Query Language)[5][6][7][8] 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). It is particularly useful in handling structured data where there are relations between different entities/variables of the data. SQL offers two main advantages over older read/write APIs like ISAM or VSAM. 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.g. with or without an index.

Originally based upon relational algebra and tuple relational calculus, SQL consists of many types of statements,[9] which may be informally classed as sublanguages, commonly: a data query language (DQL),[a] a data definition language (DDL),[b] a data control language (DCL), and a data manipulation language (DML).[c][10] 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 often described as, and to a great extent is, a declarative language (4GL), it also includes procedural elements.

SQL was one of the first commercial languages for 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".[11] Despite not entirely adhering to the relational model as described by Codd, it became the most widely used database language.[12][13]

SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standardization (ISO) in 1987.[14] 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.

SQL
ParadigmMulti-paradigm: declarative
FamilyProgramming language
Designed byDonald D. Chamberlin
Raymond F. Boyce
DeveloperISO/IEC
First appeared1974
Typing disciplineStatic, strong
OSCross-platform
File formatsFile format details
Filename extension.sql
Internet media typeapplication/sql[1][2]
Developed byISO/IEC
Initial release1986
Latest release
SQL:2016
(December 2016)
Type of formatDatabase
StandardISO/IEC 9075
Open format?Yes
Major implementations
Many
Dialects
  • SQL-86
  • SQL-89
  • SQL-92
  • SQL:1999
  • SQL:2003
  • SQL:2006
  • SQL:2008
  • SQL:2011
  • SQL:2016
Influenced by
Datalog
Influenced
CQL, LINQ, SOQL, PowerShell,[3] JPQL, jOOQ, N1QL

History

SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce after learning about the relational model from Ted Codd[15] in the early 1970s.[16] 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 1970s.[16]

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.[15] The acronym SEQUEL was later changed to SQL because "SEQUEL" was a trademark of the UK-based Hawker Siddeley Dynamics Engineering Limited company.[17]

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 DB2, which were commercially available in 1979, 1981, and 1983, respectively.[18]

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, Inc. introduced the first commercially available implementation 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,[15] and most recently, 2016.

Design

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 strictly returns to the original foundation: for example, see The Third Manifesto. However, no known proof exists that such uniqueness cannot be added to SQL itself, or at least a variation of SQL. In other words, it's quite possible that SQL can be "fixed" or at least improved in this regard such that the industry may not have to switch to a completely different query language to obtain uniqueness. Debate on this remains open.

Syntax

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.)[19]
  • 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 extensions

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:

Source Common name Full name
ANSI/ISO Standard SQL/PSM SQL/Persistent Stored Modules
Interbase / Firebird PSQL Procedural SQL
IBM DB2 SQL PL SQL Procedural Language (implements SQL/PSM)
IBM Informix SPL Stored Procedural Language
IBM Netezza NZPLSQL[20] (based on Postgres PL/pgSQL)
Invantive PSQL[21] Invantive Procedural SQL (implements SQL/PSM and PL/SQL)
Microsoft / Sybase T-SQL Transact-SQL
Mimer SQL SQL/PSM SQL/Persistent Stored Module (implements SQL/PSM)
MySQL SQL/PSM SQL/Persistent Stored Module (implements SQL/PSM)
MonetDB SQL/PSM SQL/Persistent Stored Module (implements SQL/PSM)
NuoDB SSP Starkey Stored Procedures
Oracle PL/SQL Procedural Language/SQL (based on Ada)
PostgreSQL PL/pgSQL Procedural Language/PostgreSQL Structured Query Language (implements SQL/PSM)
SAP R/3 ABAP Advanced Business Application Programming
SAP HANA SQLScript SQLScript
Sybase Watcom-SQL SQL Anywhere Watcom-SQL Dialect
Teradata SPL Stored Procedural Language

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 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.[22]

Interoperability and standardization

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 PostgreSQL[23] and Mimer SQL[24] which strive for standards compliance, though PostgreSQL does not adhere to the standard in how folding of unquoted names is done. The folding of unquoted names to lower case in PostgreSQL is incompatible with the SQL standard,[25] which says that unquoted names should be folded to upper case.[26] Thus, Foo should be equivalent to FOO not foo according to the standard.

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,[27][28] and lacks a TIME type)[29] and MS SQL Server (before the 2008 version). 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.g. indexes, file storage...), leaving implementations to decide how to behave.
  • 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 1986 as SQL-86[30] and the International Organization for Standardization (ISO) in 1987. It is maintained by ISO/IEC JTC 1, Information technology, Subcommittee SC 32, Data management and interchange. The standard is commonly denoted by the pattern: ISO/IEC 9075-n:yyyy Part n: title, or, as a shortcut, ISO/IEC 9075.

ISO/IEC 9075 is complemented by ISO/IEC 13249: 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 1996, 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.[31]

The original standard declared that the official pronunciation for "SQL" was an initialism: /ˌɛsˌkjuːˈɛl/ ("ess cue el").[12] Regardless, many English-speaking database professionals (including Donald Chamberlin himself[32]) use the acronym-like pronunciation of /ˈsiːkwəl/ ("sequel"),[33] mirroring the language's pre-release development name of "SEQUEL".[16][17][32][16] The SQL standard has gone through a number of revisions:

Year Name Alias Comments
1986 SQL-86 SQL-87 First formalized by ANSI.
1989 SQL-89 FIPS 127-1 Minor revision that added integrity constraints, adopted as FIPS 127-1.
1992 SQL-92 SQL2, FIPS 127-2 Major revision (ISO 9075), Entry Level SQL-92 adopted as FIPS 127-2.
1999 SQL:1999 SQL3 Added regular expression matching, recursive queries (e.g. transitive closure), triggers, support for procedural and control-of-flow statements, non-scalar types (arrays), and some object-oriented features (e.g. structured types). Support for embedding SQL in Java (SQL/OLB) and vice versa (SQL/JRT).
2003 SQL:2003 Introduced XML-related features (SQL/XML), window functions, standardized sequences, and columns with auto-generated values (including identity-columns).
2006 SQL:2006 ISO/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. In addition, it lets applications integrate queries into their SQL code with XQuery, the XML Query Language published by the World Wide Web Consortium (W3C), to concurrently access ordinary SQL-data and XML documents.[34]
2008 SQL:2008 Legalizes ORDER BY outside cursor definitions. Adds INSTEAD OF triggers, TRUNCATE statement,[35] FETCH clause.
2011 SQL:2011 Adds temporal data (PERIOD FOR)[36] (more information at: Temporal database#History). Enhancements for window functions and FETCH clause.[37]
2016 SQL:2016 Adds row pattern matching, polymorphic table functions, JSON.

Interested parties may purchase SQL standards documents from ISO,[38] IEC or ANSI. A draft of SQL:2008 is freely available as a zip archive.[39]

The SQL standard is divided into nine parts.

  • ISO/IEC 9075-1:2016 Part 1: Framework (SQL/Framework). It provides logical concepts.
  • ISO/IEC 9075-2:2016 Part 2: Foundation (SQL/Foundation). It contains the most central elements of the language and consists of both mandatory and optional features.
  • ISO/IEC 9075-3:2016 Part 3: Call-Level Interface (SQL/CLI). It defines interfacing components (structures, procedures, variable bindings) that can be used to execute SQL statements from applications written in Ada, C respectively C++, COBOL, Fortran, MUMPS, Pascal or PL/I. (For Java see part 10.) SQL/CLI is defined in such a way that SQL statements and SQL/CLI procedure calls are treated as separate from the calling application's source code. Open Database Connectivity is a well-known superset of SQL/CLI. This part of the standard consists solely of mandatory features.
  • ISO/IEC 9075-4:2016 Part 4: Persistent stored modules (SQL/PSM). 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. In addition, SQL/PSM formalizes declaration and maintenance of persistent database language routines (e.g., "stored procedures"). This part of the standard consists solely of optional features.
  • Part-6: Support for JavaScript Object Notation (JSON). In 2017 ISO/IEC published a first technical report about the effort to integrate the data type JSON into the SQL standard. Please consider that technical reports reflects the current state of the discussion and are not part of the standard.
  • ISO/IEC 9075-9:2016 Part 9: Management of External Data (SQL/MED). It provides extensions to SQL that define foreign-data wrappers and datalink types to allow SQL to manage external data. External data is data that is accessible to, but not managed by, an SQL-based DBMS. This part of the standard consists solely of optional features.
  • ISO/IEC 9075-10:2016 Part 10: Object language bindings (SQL/OLB). It defines the syntax and semantics of SQLJ, which is SQL embedded in Java (see also part 3). The standard also describes mechanisms to ensure binary portability of SQLJ applications, and specifies various Java packages and their contained classes. This part of the standard consists solely of optional features. Unlike SQL/OLB JDBC defines an API and is not part of the SQL standard.
  • ISO/IEC 9075-11:2016 Part 11: Information and definition schemas (SQL/Schemata). It defines the Information Schema and Definition Schema, providing a common set of tools to make SQL databases and objects self-describing. These tools include the SQL object identifier, structure and integrity constraints, security and authorization specifications, features and packages of ISO/IEC 9075, support of features provided by SQL-based DBMS implementations, SQL-based DBMS implementation information and sizing items, and the values supported by the DBMS implementations.[40] This part of the standard contains both mandatory and optional features.
  • ISO/IEC 9075-13:2016 Part 13: SQL Routines and types using the Java TM programming language (SQL/JRT). It specifies the ability to invoke static Java methods as routines from within SQL applications ('Java-in-the-database'). It also calls for the ability to use Java classes as SQL structured user-defined types. This part of the standard consists solely of optional features.
  • ISO/IEC 9075-14:2016 Part 14: XML-Related Specifications (SQL/XML). It specifies SQL-based extensions for using XML in conjunction with SQL. The XML data type is introduced, as well as several routines, functions, and XML-to-SQL data type mappings to support manipulation and storage of XML in an SQL database.[34] This part of the standard consists solely of optional features.

ISO/IEC 9075 is complemented by ISO/IEC 13249 SQL Multimedia and Application Packages. This closely related but separate standard is developed by the same committee. It defines interfaces and packages based on SQL. The aim is a unified access to typical database applications like text, pictures, data mining or spatial data.

  • ISO/IEC 13249-1:2016 Part 1: Framework
  • ISO/IEC 13249-2:2003 Part 2: Full-Text
  • ISO/IEC 13249-3:2016 Part 3: Spatial
  • ISO/IEC 13249-5:2003 Part 5: Still image
  • ISO/IEC 13249-6:2006 Part 6: Data mining
  • ISO/IEC 13249-7:2013 Part 7: History
  • ISO/IEC 13249-8:xxxx Part 8: Metadata Registry Access MRA (work in progress)

Alternatives

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.

Distributed SQL processing

Distributed Relational Database Architecture (DRDA) was designed by a work group within IBM in the period 1988 to 1994. DRDA enables network connected relational databases to cooperate to fulfill SQL requests.[42][43]

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.

Criticisms

Chamberlin's 2012 paper[15] discusses four historical criticisms of SQL:

Orthogonality and completeness

Early 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.[15]

NULLs

SQL's controversial "NULL" and three-value logic. Predicates evaluated over nulls return the logical value of "unknown" rather than true or false. Features such as outer-join depend on nulls.

Duplicates

Other popular critiques are that it allows duplicate rows, making integration with languages such as Python, whose data types might make it difficult to accurately represent the data,[15] difficult in terms of parsing and by the absence of modularity.[44]

Impedence Mismatch

In a similar sense to Object-relational impedance mismatch, there is a mismatch between the declarative SQL language and the procedural languages that SQL is typically embedded in.

See also

  • Portal-puzzle.svg SQL portal

Notes

  1. ^ Formally, "SQL-data" statements excluding "SQL-data change" statements; this is primarily the Select statement.
  2. ^ Formally, "SQL-schema" statements.
  3. ^ Formally, "SQL-data change" statements

References

  1. ^ "Media Type registration for application/sql". Internet Assigned Numbers Authority. 10 April 2013. Retrieved 10 April 2013.
  2. ^ "The application/sql Media Type, RFC 6922". Internet Engineering Task Force. April 2013. p. 3. Retrieved 10 April 2013.
  3. ^ Paul, Ryan. "A guided tour of the Microsoft Command Shell". Ars Technica. Retrieved 10 April 2011.
  4. ^ Beaulieu, Alan (April 2009). Mary E Treseler, ed. Learning SQL (2nd ed.). Sebastapol, CA, USA: O'Reilly. ISBN 978-0-596-52083-0.
  5. ^ "SQL". Britannica.com. Retrieved 2013-04-02.
  6. ^ "SQL". Oxforddictionaries.com. Retrieved 2017-01-16.
  7. ^ "SQL Guide". Publib.boulder.ibm.com. Retrieved 2017-01-16.
  8. ^ "Structured Query Language (SQL)". Msdn.microsoft.com. Retrieved 2017-01-16.
  9. ^ SQL-92, 4.22 SQL-statements, 4.22.1 Classes of SQL-statements "There are at least five ways of classifying SQL-statements:", 4.22.2, SQL statements classified by function "The following are the main classes of SQL-statements:"; SQL:2003 4.11 SQL-statements, and later revisions.
  10. ^ Chatham, Mark (2012). Structured Query Language By Example - Volume I: Data Query Language. p. 8. ISBN 978-1-29119951-2.
  11. ^ Codd, Edgar F. (June 1970). "A Relational Model of Data for Large Shared Data Banks". Communications of the ACM. 13 (6): 377–87. CiteSeerX 10.1.1.88.646. doi:10.1145/362384.362685.
  12. ^ a b Chapple, Mike. "SQL Fundamentals". Databases. About.com. Retrieved 2009-01-28.
  13. ^ "Structured Query Language (SQL)". International Business Machines. October 27, 2006. Retrieved 2007-06-10.
  14. ^ "ISO/IEC 9075-1:2016: Information technology – Database languages – SQL – Part 1: Framework (SQL/Framework)".
  15. ^ a b c d e f Chamberlin, Donald (2012). "Early History of SQL". IEEE Annals of the History of Computing. 34 (4): 78–82. doi:10.1109/MAHC.2012.61. Retrieved 3 February 2018.
  16. ^ a b c d Chamberlin, Donald D; Boyce, Raymond F (1974). "SEQUEL: A Structured English Query Language" (PDF). Proceedings of the 1974 ACM SIGFIDET Workshop on Data Description, Access and Control. Association for Computing Machinery: 249–64. Retrieved 2007-06-09.
  17. ^ a b Oppel, Andy (February 27, 2004). Databases Demystified. San Francisco, CA: McGraw-Hill Osborne Media. pp. 90–1. ISBN 978-0-07-146960-9.
  18. ^ "History of IBM, 1978". IBM Archives. IBM. Retrieved 2007-06-09.
  19. ^ ANSI/ISO/IEC International Standard (IS). Database Language SQL—Part 2: Foundation (SQL/Foundation). 1999.
  20. ^ "IBM PureData System for Analytics, Version 7.0.3".
  21. ^ "Invantive Procedural SQL".
  22. ^ PostgreSQL contributors (2011). "PostgreSQL server programming". PostgreSQL 9.1 official documentation. postgresql.org. Retrieved 2012-03-09.
  23. ^ PostgreSQL contributors (2012). "About PostgreSQL". PostgreSQL 9.1 official website. PostgreSQL Global Development Group. Retrieved March 9, 2012. PostgreSQL prides itself in standards compliance. Its SQL implementation strongly conforms to the ANSI-SQL:2008 standard
  24. ^ "Mimer SQL, Built on Standards". Mimer SQL official website. Mimer Information Technology. 2009.
  25. ^ "4.1. Lexical Structure". PostgreSQL documentation. 2018.
  26. ^ "(Second Informal Review Draft) ISO/IEC 9075:1992, Database Language SQL, Section 5.2, syntax rule 11". 30 July 1992.
  27. ^ Lorentz, Diana; Roeser, Mary Beth; Abraham, Sundeep; Amor, Angela; Arora, Geeta; Arora, Vikas; Ashdown, Lance; Baer, Hermann; Bellamkonda, Shrikanth (October 2010) [1996]. "Basic Elements of Oracle SQL: Data Types". Oracle Database SQL Language Reference 11g Release 2 (11.2). Oracle Database Documentation Library. Redwood City, CA: Oracle USA, Inc. Retrieved December 29, 2010. For each DATE value, Oracle stores the following information: century, year, month, date, hour, minute, and second
  28. ^ Lorentz, Diana; Roeser, Mary Beth; Abraham, Sundeep; Amor, Angela; Arora, Geeta; Arora, Vikas; Ashdown, Lance; Baer, Hermann; Bellamkonda, Shrikanth (October 2010) [1996]. "Basic Elements of Oracle SQL: Data Types". Oracle Database SQL Language Reference 11g Release 2 (11.2). Oracle Database Documentation Library. Redwood City, CA: Oracle USA, Inc. Retrieved December 29, 2010. The datetime data types are DATE...
  29. ^ Lorentz, Diana; Roeser, Mary Beth; Abraham, Sundeep; Amor, Angela; Arora, Geeta; Arora, Vikas; Ashdown, Lance; Baer, Hermann; Bellamkonda, Shrikanth (October 2010) [1996]. "Basic Elements of Oracle SQL: Data Types". Oracle Database SQL Language Reference 11g Release 2 (11.2). Oracle Database Documentation Library. Redwood City, CA: Oracle USA, Inc. Retrieved December 29, 2010. Do not define columns with the following SQL/DS and DB2 data types, because they have no corresponding Oracle data type:... TIME
  30. ^ "Finding Aid". X3H2 Records, 1978–95. American National Standards Institute.
  31. ^ Doll, Shelley (June 19, 2002). "Is SQL a Standard Anymore?". TechRepublic's Builder.com. TechRepublic. Archived from the original on 2012-07-05. Retrieved 2016-04-12.
  32. ^ a b Gillespie, Patrick. "Pronouncing SQL: S-Q-L or Sequel?". Retrieved 12 February 2012.
  33. ^ Melton, Jim; Alan R Simon (1993). "1.2. What is SQL?". Understanding the New SQL: A Complete Guide. Morgan Kaufmann. p. 536. ISBN 978-1-55860-245-8. SQL (correctly pronounced "ess cue ell," instead of the somewhat common "sequel")...
  34. ^ a b Wagner, Michael (2010). SQL/XML:2006 - Evaluierung der Standardkonformität ausgewählter Datenbanksysteme. Diplomica Verlag. p. 100. ISBN 978-3-8366-9609-8.
  35. ^ "SQL:2008 now an approved ISO international standard". Sybase. July 2008. Archived from the original on 2011-06-28.
  36. ^ Krishna Kulkarni, Jan-Eike Michels (2012). "Temporal features in SQL:2011" (PDF).
  37. ^ Fred Zemke (2012). "What's new in SQL:2011" (PDF).
  38. ^ "ISO/IEC 9075-2:2016: Information technology -- Database languages -- SQL -- Part 2: Foundation (SQL/Foundation)". December 2016.
  39. ^ "SQL:2008 draft" (Zip). Whitemarsh Information Systems Corporation.
  40. ^ "ISO/IEC 9075-11:2008: Information and Definition Schemas (SQL/Schemata)". 2008: 1.
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Sources

SQL standards documents

ITTF publicly available standards and technical reports

The ISO/IEC Information Technology Task Force publishes publicly available standards including SQL. Technical Corrigenda (corrections) and Technical Reports (discussion documents) are published there.

SQL -- Part 1: Framework (SQL/Framework)

Draft documents

Formal SQL standards are available from ISO and ANSI for a fee. For informative use, as opposed to strict standards compliance, late drafts often suffice.

External links

Data definition language

A data definition or data description language (DDL) is a syntax similar to a computer programming language for defining data structures, especially database schemas. DDL statements create, modify, and remove database objects such as tables, indexes, and users. Common DDL statements are CREATE, ALTER, and DROP

Database transaction

A transaction symbolizes a unit of work performed within a database management system (or similar system) against a database, and treated in a coherent and reliable way independent of other transactions. A transaction generally represents any change in a database. Transactions in a database environment have two main purposes:

To provide reliable units of work that allow correct recovery from failures and keep a database consistent even in cases of system failure, when execution stops (completely or partially) and many operations upon a database remain uncompleted, with unclear status.

To provide isolation between programs accessing a database concurrently. If this isolation is not provided, the programs' outcomes are possibly erroneous.In a Database Management System, a transaction is a single unit of logic or work, sometimes made up of multiple operations. Any logical calculation done in a consistent mode in a database is known as a transaction. One example is a transfer from one bank account to another: the complete transaction requires subtracting the amount to be transferred from one account and adding that same amount to the other.

A database transaction, by definition, must be atomic, consistent, isolated and durable. Database practitioners often refer to these properties of database transactions using the acronym ACID.

Transactions provide an "all-or-nothing" proposition, stating that each work-unit performed in a database must either complete in its entirety or have no effect whatsoever. Further, the system must isolate each transaction from other transactions, results must conform to existing constraints in the database, and transactions that complete successfully must get written to durable storage.

Join (SQL)

An SQL join clause - corresponding to a join operation in relational algebra - combines columns from one or more tables in a relational database. It creates a set that can be saved as a table or used as it is. A JOIN is a means for combining columns from one (self-join) or more tables by using values common to each. ANSI-standard SQL specifies five types of JOIN: INNER, LEFT OUTER, RIGHT OUTER, FULL OUTER and CROSS. As a special case, a table (base table, view, or joined table) can JOIN to itself in a self-join.

A programmer declares a JOIN statement to identify rows for joining. If the evaluated predicate is true, the combined row is then produced in the expected format, a row set or a temporary table.

List of content management systems

This is a list of notable content management systems that are used to organize and facilitate collaborative content creation. Many of them are built on top of separate content management frameworks.

Microsoft Access

Microsoft Access is a database management system (DBMS) from Microsoft that combines the relational Microsoft Jet Database Engine with a graphical user interface and software-development tools. It is a member of the Microsoft Office suite of applications, included in the Professional and higher editions or sold separately.

Microsoft Access stores data in its own format based on the Access Jet Database Engine. It can also import or link directly to data stored in other applications and databases.Software developers, data architects and power users can use Microsoft Access to develop application software. Like other Microsoft Office applications, Access is supported by Visual Basic for Applications (VBA), an object-based programming language that can reference a variety of objects including DAO (Data Access Objects), ActiveX Data Objects, and many other ActiveX components. Visual objects used in forms and reports expose their methods and properties in the VBA programming environment, and VBA code modules may declare and call Windows operating system operations.

Microsoft Azure

Microsoft Azure (formerly Windows Azure ) is a cloud computing service created by Microsoft for building, testing, deploying, and managing applications and services through Microsoft-managed data centers. It provides software as a service (SaaS), platform as a service (PaaS) and infrastructure as a service (IaaS) and supports many different programming languages, tools and frameworks, including both Microsoft-specific and third-party software and systems.

Azure was announced in October 2008, started with codename "Project Red Dog", and released on February 1, 2010, as "Windows Azure" before being renamed "Microsoft Azure" on March 25, 2014.

Microsoft SQL Server

Microsoft SQL Server is a relational database management system developed by Microsoft. As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications—which may run either on the same computer or on another computer across a network (including the Internet).

Microsoft markets at least a dozen different editions of Microsoft SQL Server, aimed at different audiences and for workloads ranging from small single-machine applications to large Internet-facing applications with many concurrent users.

MySQL

MySQL ( "My S-Q-L") is an open source relational database management system (RDBMS). Its name is a combination of "My", the name of co-founder Michael Widenius's daughter, and "SQL", the abbreviation for Structured Query Language.

MySQL is free and open-source software under the terms of the GNU General Public License, and is also available under a variety of proprietary licenses. MySQL was owned and sponsored by the Swedish company MySQL AB, which was bought by Sun Microsystems (now Oracle Corporation). In 2010, when Oracle acquired Sun, Widenius forked the open-source MySQL project to create MariaDB.

MySQL is a component of the LAMP web application software stack (and others), which is an acronym for Linux, Apache, MySQL, Perl/PHP/Python. MySQL is used by many database-driven web applications, including Drupal, Joomla, phpBB, and WordPress. MySQL is also used by many popular websites, including Google (though not for searches), Facebook, Twitter, Flickr, and YouTube.

NoSQL

A NoSQL (originally referring to "non SQL" or "non relational") database provides a mechanism for storage and retrieval of data that is modeled in means other than the tabular relations used in relational databases. Such databases have existed since the late 1960s, but did not obtain the "NoSQL" moniker until a surge of popularity in the early 21st century, triggered by the needs of Web 2.0 companies. NoSQL databases are increasingly used in big data and real-time web applications. NoSQL systems are also sometimes called "Not only SQL" to emphasize that they may support SQL-like query languages, or sit alongside SQL database in a polyglot persistence architecture.Motivations for this approach include: simplicity of design, simpler "horizontal" scaling to clusters of machines (which is a problem for relational databases), and finer control over availability. The data structures used by NoSQL databases (e.g. key-value, wide column, graph, or document) are different from those used by default in relational databases, making some operations faster in NoSQL. The particular suitability of a given NoSQL database depends on the problem it must solve. Sometimes the data structures used by NoSQL databases are also viewed as "more flexible" than relational database tables.Many NoSQL stores compromise consistency (in the sense of the CAP theorem) in favor of availability, partition tolerance, and speed. Barriers to the greater adoption of NoSQL stores include the use of low-level query languages (instead of SQL, for instance the lack of ability to perform ad-hoc joins across tables), lack of standardized interfaces, and huge previous investments in existing relational databases. Most NoSQL stores lack true ACID transactions, although a few databases have made them central to their designs.

Instead, most NoSQL databases offer a concept of "eventual consistency" in which database changes are propagated to all nodes "eventually" (typically within milliseconds) so queries for data might not return updated data immediately or might result in reading data that is not accurate, a problem known as stale reads. Additionally, some NoSQL systems may exhibit lost writes and other forms of data loss. Some NoSQL systems provide concepts such as write-ahead logging to avoid data loss. For distributed transaction processing across multiple databases, data consistency is an even bigger challenge that is difficult for both NoSQL and relational databases. Even current relational databases "do not allow referential integrity constraints to span databases." There are few systems that maintain both ACID transactions and X/Open XA standards for distributed transaction processing.

Object-relational mapping

Object-relational mapping (ORM, O/RM, and O/R mapping tool) in computer science is a programming technique for converting data between incompatible type systems using object-oriented programming languages. This creates, in effect, a "virtual object database" that can be used from within the programming language. There are both free and commercial packages available that perform object-relational mapping, although some programmers opt to construct their own ORM tools.

In object-oriented programming, data-management tasks act on objects that are almost always non-scalar values. For example, an address book entry that represents a single person along with zero or more phone numbers and zero or more addresses. This could be modeled in an object-oriented implementation by a "Person object" with attributes/fields to hold each data item that the entry comprises: the person's name, a list of phone numbers, and a list of addresses. The list of phone numbers would itself contain "PhoneNumber objects" and so on. The address-book entry is treated as a single object by the programming language (it can be referenced by a single variable containing a pointer to the object, for instance). Various methods can be associated with the object, such as a method to return the preferred phone number, the home address, and so on.

However, many popular database products such as SQL database management systems (DBMS) can only store and manipulate scalar values such as integers and strings organized within tables. The programmer must either convert the object values into groups of simpler values for storage in the database (and convert them back upon retrieval), or only use simple scalar values within the program. Object-relational mapping implements the first approach.The heart of the problem involves translating the logical representation of the objects into an atomized form that is capable of being stored in the database while preserving the properties of the objects and their relationships so that they can be reloaded as objects when needed. If this storage and retrieval functionality is implemented, the objects are said to be persistent.

Open Database Connectivity

In computing, Open Database Connectivity (ODBC) is a standard application programming interface (API) for accessing database management systems (DBMS). The designers of ODBC aimed to make it independent of database systems and operating systems. An application written using ODBC can be ported to other platforms, both on the client and server side, with few changes to the data access code.

ODBC accomplishes DBMS independence by using an ODBC driver as a translation layer between the application and the DBMS. The application uses ODBC functions through an ODBC driver manager with which it is linked, and the driver passes the query to the DBMS. An ODBC driver can be thought of as analogous to a printer driver or other driver, providing a standard set of functions for the application to use, and implementing DBMS-specific functionality. An application that can use ODBC is referred to as "ODBC-compliant". Any ODBC-compliant application can access any DBMS for which a driver is installed. Drivers exist for all major DBMSs, many other data sources like address book systems and Microsoft Excel, and even for text or comma-separated values (CSV) files.

ODBC was originally developed by Microsoft and Simba Technologies during the early 1990s, and became the basis for the Call Level Interface (CLI) standardized by SQL Access Group in the Unix and mainframe field. ODBC retained several features that were removed as part of the CLI effort. Full ODBC was later ported back to those platforms, and became a de facto standard considerably better known than CLI. The CLI remains similar to ODBC, and applications can be ported from one platform to the other with few changes.

PL/SQL

PL/SQL (Procedural Language for SQL) is Oracle Corporation's procedural extension for SQL and the Oracle relational database. PL/SQL is available in Oracle Database (since version 6 - stored PL/SQL procedures/functions/packages/triggers since version 7), TimesTen in-memory database (since version 11.2.1), and IBM DB2 (since version 9.7). Oracle Corporation usually extends PL/SQL functionality with each successive release of the Oracle Database.

PL/SQL includes procedural language elements such as conditions and loops. It allows declaration of constants and variables, procedures and functions, types and variables of those types, and triggers. It can handle exceptions (runtime errors). Arrays are supported involving the use of PL/SQL collections. Implementations from version 8 of Oracle Database onwards have included features associated with object-orientation. One can create PL/SQL units such as procedures, functions, packages, types, and triggers, which are stored in the database for reuse by applications that use any of the Oracle Database programmatic interfaces.

PostgreSQL

PostgreSQL, often simply Postgres, is an open source object-relational database management system (ORDBMS) with an emphasis on extensibility and standards compliance. It can handle workloads ranging from small single-machine applications to large Internet-facing applications (or for data warehousing) with many concurrent users. It is the default database on macOS Server and is available for Microsoft Windows and Linux (supplied in most distributions).

PostgreSQL is ACID-compliant and transactional. PostgreSQL has updatable views and materialized views, triggers, foreign keys; supports functions and stored procedures, and other expandability.PostgreSQL is developed by the PostgreSQL Global Development Group, a diverse group of many companies and individual contributors. It is free and open-source, released under the terms of the PostgreSQL License, a permissive software license.

Relational database

A relational database is a digital database based on the relational model of data, as proposed by E. F. Codd in 1970.

A software system used to maintain relational databases is a relational database management system (RDBMS). Virtually all relational database systems use SQL (Structured Query Language) for querying and maintaining the database.

Rollback (data management)

In database technologies, a rollback is an operation which returns the database to some previous state. Rollbacks are important for database integrity, because they mean that the database can be restored to a clean copy even after erroneous operations are performed. They are crucial for recovering from database server crashes; by rolling back any transaction which was active at the time of the crash, the database is restored to a consistent state.

The rollback feature is usually implemented with a transaction log, but can also be implemented via multiversion concurrency control.

SQL Server Compact

Microsoft SQL Server Compact (SQL CE) is a compact relational database produced by Microsoft for applications that run on mobile devices and desktops. Prior to the introduction of the desktop platform, it was known as SQL Server for Windows CE and SQL Server Mobile Edition.

It includes both 32-bit and 64-bit native support. SQL CE targets occasionally connected applications and applications with an embedded database. It is free to download and redistribute. An ODBC driver for SQL CE does not exist, nor is one planned. Native applications may use SQL CE via OLE DB.

The latest, and last, release is the SQL Server Compact 4.0. As of February 2013 SQL Server Compact Edition had been deprecated; no new versions or updates are planned, although Microsoft will continue to support until July 2021.

SQL injection

SQL injection is a code injection technique, used to attack data-driven applications, in which nefarious SQL statements are inserted into an entry field for execution (e.g. to dump the database contents to the attacker). SQL injection must exploit a security vulnerability in an application's software, for example, when user input is either incorrectly filtered for string literal escape characters embedded in SQL statements or user input is not strongly typed and unexpectedly executed. SQL injection is mostly known as an attack vector for websites but can be used to attack any type of SQL database.

SQL injection attacks allow attackers to spoof identity, tamper with existing data, cause repudiation issues such as voiding transactions or changing balances, allow the complete disclosure of all data on the system, destroy the data or make it otherwise unavailable, and become administrators of the database server.

In a 2012 study, it was observed that the average web application received 4 attack campaigns per month, and retailers received twice as many attacks as other industries.

SQLite

SQLite (, ) is a relational database management system contained in a C programming library. In contrast to many other database management systems, SQLite is not a client–server database engine. Rather, it is embedded into the end program.

SQLite is ACID-compliant and implements most of the SQL standard, generally following PostgreSQL syntax. However, SQLite uses a dynamically and weakly typed SQL syntax that does not guarantee the domain integrity. This means that one can, for example, insert a string into a column defined as an integer. SQLite will attempt to convert data between formats where appropriate, the string "123" into an integer in this case, but does not guarantee such conversions, and will store the data as-is if such a conversion is not possible.

SQLite is a popular choice as embedded database software for local/client storage in application software such as web browsers. It is arguably the most widely deployed database engine, as it is used today by several widespread browsers, operating systems, and embedded systems (such as mobile phones), among others. SQLite has bindings to many programming languages.

Simple Features

Simple Features (officially Simple Feature Access) is both an Open Geospatial Consortium (OGC) and International Organization for Standardization (ISO) standard ISO 19125 that specifies a common storage and access model of mostly two-dimensional geometries (point, line, polygon, multi-point, multi-line, etc.) used by geographic information systems.

The ISO 19125 standard comes in two parts. Part one, ISO 19125-1 (SFA-CA for "common architecture"), defines a model for two-dimensional simple features, with linear interpolation between vertices. The data model defined in SFA-CA is a hierarchy of classes. This part also defines representation using Well-Known Text (and Binary). Part 2 of the standard, ISO 19125-2 (SFA-SQL), defines an implementation using SQL. The OpenGIS standard(s) cover implementations in CORBA and OLE/COM as well, although these have lagged behind the SQL one and are not standardized by ISO.

The ISO/IEC 13249-3 SQL/MM Spatial extends the Simple Features data model mainly with circular interpolations (e.g. circular arcs) and adds other features like coordinate transformations and methods for validating geometries as well as Geography Markup Language support.

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