A relational data language that provides a consistent, English keyword-oriented set of facilities for query, data definition, data manipulation and data control. It is a programmed interface to relational database management systems (RDBMSs). IBM introduced SQL as the main external interface to its experimental RDBMS, System R, which it developed in the 1970s. SQL statements include:
• Data manipulation language statements: SELECT, INSERT, UPDATE and DELETE
• Data definition language statements, including the CREATE and DROP statements for tables and indexes
• Statements that control data consistency, and grant and revoke authority
SQL statements are called “dynamic” when they are not completely specified until the program is executed. They are called “static” when they are completely specified when the program is compiled. SQL is precise, because it is based on predicate logic, but is difficult for average users to deal with, and its most fruitful position is as a protocol for software-to-software connectivity, rather than for human-to-software access.