SQL (/ˌɛsˌkjuːˈɛl/ (About this soundlisten) S-Q-L, /ˈsiːkwəl/ "sequel"; Structured Query Language) 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, 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] 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, it 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 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.
Devon(/ˈdɛvən/, also known asDevonshire) is acountyofEngland, reaching from theBristol Channelin the north to theEnglish Channelin the south. It is part ofSouth West England, bounded byCornwallto the west,Somersetto the north-east andDorsetto the east. The city ofExeteris thecounty town. The county includes the districts ofEast Devon,Mid Devon,North Devon,South Hams,Teignbridge,TorridgeandWest Devon.PlymouthandTorbayare each geographically part of Devon, but are administered asunitary authorities.Combined as aceremonial county, Devon's area is 6,707 km2(2,590 square miles)and its population is about 1.1 million.
Devon derives its name fromDumnonia(the shift frommtovis a typicalCeltic consonant shift). During theBritish Iron Age,Roman Britainand theearly Middle Ages, this was the homeland of theDumnoniiBrittonicCelts. TheAnglo-Saxon settlement of Britainresulted in the partial assimilation of Dumnonia into theKingdom of Wessexduring the eighth and ninth centuries. The western boundary with Cornwall was set at theRiver TamarbyKing Æthelstanin 936. Devon was later constituted as ashireof theKingdom of England.
The north and south coasts of Devon each have both cliffs and sandy shores, and the county'sbayscontainseaside resorts,fishing townsandports. The inland terrain is rural, generally hilly and has a lower population density than many other parts of England.Dartmooris the largest open space in southern England, at 954 km2(368 square miles);itsmoorlandextends across a large expanse ofgranitebedrock. To the north of Dartmoor are theCulm MeasuresandExmoor. In the valleys and lowlands of south and east Devon the soil is more fertile, drained by rivers including theExe, theCulm, theTeign, theDartand theOtter.
As well as agriculture, much of theeconomy of Devonis based ontourism. The comparatively mild climate, coastline and landscape make Devon a destination forrecreation and leisure in England. Visitors are particularly attracted to the Dartmoor and Exmoornational parks; its coasts, including the resort towns along the south coast known collectively as theEnglish Riviera; theJurassic CoastandNorth Devon's UNESCO Biosphere Reserve; and the countryside including theCornwall and West Devon Mining Landscape.