Basic Query Structure SQL is based on set and relational operations with certain modifications and enhancements A typical SQL query has the form: select A1,A2,..,An from r1,f2,,「m where P A,represents an attribute R,represents a relation P is a predicate. This query is equivalent to the relational algebra expression. Π4.A2A(o(化×r2×…×rm)》 The result of an SQL query is a relation. Database System Concepts,5th Edition,Oct 5,2006 3.9 ©Silberschat乜，Korth and SudarshanDatabase System Concepts, 5 3.9 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 Basic Query Structure SQL is based on set and relational operations with certain modifications and enhancements A typical SQL query has the form: select A1 , A2 , ..., An from r1 , r2 , ..., rm where P Ai represents an attribute Ri represents a relation P is a predicate. This query is equivalent to the relational algebra expression. The result of an SQL query is a relation. ( ( )) A1 ,A2 , ,A P 1 2 m r r r n     