SQL became a standard of the American National Standards Institute (ANSI) in 1986 and of the International Organization for Standardization (ISO) in 1987. Despite not entirely adhering to the relational model as described by Codd, SQL became the most widely used database language. The model was described in his influential 1970 paper, "A Relational Model of Data for Large Shared Data Banks". SQL was one of the first commercial languages to use Edgar F. Although SQL is essentially a declarative language ( 4GL), it also includes procedural elements.
The scope of SQL includes data query, data manipulation (insert, update, and delete), data definition ( schema creation and modification), and data access control.
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 data definition language (DDL), a data control language (DCL), and a data manipulation language (DML). Secondly, it eliminates the need to specify how to reach a record, i.e., with or without an index. Firstly, it introduced the concept of accessing many records with one single command.
Introduced in the 1970s, SQL offered two main advantages over older read–write APIs such as ISAM or VSAM. It is particularly useful in handling structured data, i.e., data incorporating relations among entities and variables. Structured Query Language ( SQL) ( / ˌ ɛ s ˌ k juː ˈ ɛ l/ ( listen) S-Q-L, sometimes / ˈ s iː k w əl/ "sequel" for historical reasons), 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).
0 kommentar(er)
