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SQL (/ˌɛsˌkjuːˈɛl/ (About this soundlisten) S-Q-L,[4] /ˈsiːkwəl/ "sequel"; Structured Query Language)[5] 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, i.e. data incorporating relations among entities and variables.
SQL offers 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, e.g. with or without an index.
Originally based upon relational algebra and tuple relational calculus, SQL consists of many types of statements,[6] 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][7] 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".[8] Despite not entirely adhering to the relational model as described by Codd, it became the most widely used database language.[9][10]
SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standardization (ISO) in 1987.[11] Since then, the standard has been revised to include a larger set of features. Despite the existence of standards, most SQL code requires at least some changes before being ported to different database systems.
Leicester (About this soundlisten) LEH-ster) is a city and unitary authority area in the East Midlands of England, and the county town of Leicestershire. The city lies on the River Soar and close to the eastern end of the National Forest. It is to the north-east of Birmingham and Coventry, south of Nottingham, and west of Peterborough.
The 2016 mid year estimate of the population of the City of Leicester unitary authority was 348,300, an increase of approximately 18,500 (Increase 5.6%) from the 2011 census figure of 329,839, making it the most populous municipality in the East Midlands region. The associated urban area is also the 11th most populous in England and the 13th most populous in the United Kingdom.
Leicester is at the intersection of two major railway lines—the north–south Midland Main Line and the east/west Birmingham to London Stansted CrossCountry line; as well as the confluence of the M1/M69 motorways and the A6/A46 trunk routes. Leicester is the home to football club Leicester City and rugby club Leicester Tigers.
