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Views

Views. Automatic View Modifications. Automatic View Modifications. Modifying views Once V defined, want to modify V like any table Modifications to V rewritten to modify base tables Unlike queries, cannot be automated in general. Automatic View Modifications.

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Views

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  1. Views Automatic View Modifications

  2. Automatic View Modifications Modifying views • Once V defined, want to modify V like any table • Modifications to V rewritten to modify base tables • Unlike queries, cannot be automated in general

  3. Automatic View Modifications Modifications to V rewritten to modify base tables (1) Rewriting process specified explicitly by view creator +Can handle all modifications – No guarantee of correctness (or meaningful) (2) Restrict views + modifications so that translation to base table modifications is meaningful and unambiguous + No user intervention – Restrictions are significant

  4. Automatic View Modifications Modifications to V rewritten to modify base tables (2) Restrict views + modifications so that translation to base table modifications is meaningful and unambiguous + No user intervention – Restrictions are significant Restrictions in SQL Standard for “updatable views”: 1) SELECT (no DISTINCT) on single table T 2) Attributes not in view can be NULL or have default value 3) Subqueries must not refer to T 4) No GROUPBY or aggregation

  5. Automatic View Modifications Modifications to V rewritten to modify base tables (2) Restrict views + modifications so that translation to base table modifications is meaningful and unambiguous + No user intervention – Restrictions are significant Demo: simple college admissions database College(cName,state,enrollment) Student(sID,sName,GPA,sizeHS) Apply(sID,cName,major,decision)

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