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Set Difference Operation Notation r-s Defined as: r-s={tlt∈rand tgs} Set differences must be taken between compatible relations. r and s must have the same arity attribute domains of r and s must be compatible Example:to find all courses taught in the Fall 2009 semester,but not in the Spring 2010 semester Ilcourse_id(o semester="Fall year=2009(section) Icourse_id(semester="Spring"Ayear=2010(section)) Database System Concepts-6th Edition 6.7 ©Silberschat乜,Korth and SudarshanDatabase System Concepts - 6 6.7 ©Silberschatz, Korth and Sudarshan th Edition Set Difference Operation Notation r – s Defined as: r – s = {t | t  r and t  s} Set differences must be taken between compatible relations. r and s must have the same arity attribute domains of r and s must be compatible Example: to find all courses taught in the Fall 2009 semester, but not in the Spring 2010 semester course_id ( semester=“Fall” Λ year=2009 (section)) − course_id ( semester=“Spring” Λ year=2010 (section))
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