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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.
St Neots /sɛnʔ ˈniːəts/[b] is a town and civil parish in the Huntingdonshire District of the county of Cambridgeshire, England, approximately 50 miles (80 km) north of central London. The town straddles the River Great Ouse and is served by a railway station on the East Coast Main Line. It is 14 miles (23 km) west of Cambridge, to which it is linked by the A428 arterial road. It is the largest town in Cambridgeshire and had a population of 30,811 in the 2011 census.[c]
The town is named after the Cornish monk Saint Neot, whose bones were moved to the Priory here from the hamlet of St Neot on Bodmin Moor in around 980 AD. Pilgrimage to the priory church and parish church brought prosperity to the settlement and the town was granted a market charter in 1130. In the 18th and 19th centuries the town enjoyed further prosperity through corn milling, brewing, stagecoach traffic and railways.
After the Second World War the town and its industry were chosen for rapid growth as London councils paid for new housing to be built to rehouse families from London. The first London overspill housing was completed in the early 1960s and new housing has continued at a slightly lower rate such that the population, including the areas transferred from Bedfordshire, is approximately four times that of the 1920s.
