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.
Cannock (/ˈkænək/) is a town and the administrative centre of the Cannock Chase district, as of the 2011 census, it has a population of 29,018, and is one the most populous towns in the district of Cannock Chase in the county of Staffordshire in the West Midlands region of England.
Cannock lies to the north of the West Midlands conurbation on the M6, A34 and A5 roads, and to the south of The Chase, an Area of Outstanding Natural Beauty (AONB). Cannock is served by a railway station on the Chase Line. The town comprises four district council electoral wards and the Cannock South ward includes the civil parish of Bridgtown, but the rest of Cannock is unparished.
Cannock forms part of the Cannock Built-up Area (population 86,121 in the 2011 census) which also includes Cheslyn Hay, Great Wyrley, Hednesford, Huntington, Heath Hayes and Wimblebury.