Basic 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,R,…R where p A represent attributes R represent relations P is a predicate This query is equivalent to the relational algebra expression: A1.2.An(op(R1×R2×…×Rm) The result of an sQl query is a relation(but may contain duplicates). SQL statements can be nested COMP3311 Fall 2011 CSE, HKUST Slide 4COMP3311 Fall 2011 CSE, HKUST Slide 4 Basic 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 represent attributes - Ri represent relations - P is a predicate. • This query is equivalent to the relational algebra expression: A1, A2, …, An(P (R1  R2  …  Rm)) • The result of an SQL query is a relation (but may contain duplicates). SQL statements can be nested