FIT1004 Lecture Notes - Lecture 9: Virtual Method Table
2 Jul 2018
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Lecture 9 Queries
Minus
● all distinct rows selected by the first query but not the second
Intersection
● All distinct rows selected by both queries
Views
● A virtual table with the result of a stored query as its contents
● can be based on one or more base tables or views
● Contains no data
● Why use them?
○ to restrict database access
○ to make complex queries easy
○ to allow data independence
○ to present different views of the same data
