CSE 132A Lecture Notes - Lecture 8: Data Definition Language, Foreign Key, Referential Integrity
25 Oct 2018
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Ex: increase all salaries in the toys dept by 10% Triggers - special assertions; define actions to take under certain conditions. Views - hide or restructure data for certain users. Any relation that is not in the db schema but is made visible to the user as a virtual relation . View def is not the same as creating a new relation by evaluating the query expression: The view contents is refreshed automatically when the db is updated! One view may be used in the expression defining another view. A view relation v is said to be recursive if it depends on itself! Ex: find actors playing in every movie by berto . Where berto-movies. title not in (select title from movies. Select actor from movies where actor not in. Select title from movie where director = bertolucci . Efficient view implementation (select * from not-all-berto: materialized views: physically create and maintain a view table.
