- View Vulnerabilities
- Changes to Underlying Objects
- Breaks In Chains
- Performance
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Breaks In Chains
Because views can be defined in terms of other views and tables, it's possible to wind up with a chain of objects, each dependent on another. Just as an actual chain can break at any link, so can a chain of objects. Any one of the views or tables in the chain might be redefined so that its dependent views no longer make sense.
As an example, here are three generations of views derived on the authors table.
create view number1 as select au_lname, phone from authors where zip like '94%' select * from number1 au_lname phone ---------------------------------------- ------------ Bennet 415 658-9932 Green 415 986-7020 Carson 415 548-7723 Stringer 415 843-2991 Straight 415 834-2919 Karsen 415 534-9219 MacFeather 415 354-7128 Dull 415 836-7128 Yokomoto 415 935-4228 White 408 496-7223 Hunter 415 836-7128 Locksley 415 585-4620 (12 row(s) affected) create view number2 as select au_lname, phone from number1 where au_lname > 'M' select * from number2 au_lname phone ---------------------------------------- ------------ MacFeather 415 354-7128 Straight 415 834-2919 Stringer 415 843-2991 White 408 496-7223 Yokomoto 415 935-4228 (5 row(s) affected) create view number3 as select au_lname, phone from number2 where au_lname = 'MacFeather' select * from number3 au_lname phone ---------------------------------------- ------------ MacFeather 415 354-7128 (1 row(s) affected)
What happens to number3 if you redefine number2 with different selection criteria?
A condition on a column available in number2's underlying table number1 (either au_fname or phone) works fine. The WHERE clause determines what, if any, data is seen through number3.
A condition such as a zip code matching "947nn" causes failure in creating number2 or displaying data through it because the zip column exists in neither number1 nor number2. With number2 in trouble, there's not much hope for retrieving data through number3.
Whatever you do to view number2, view number3 still exists, and becomes usable again by dropping and re-creating view number2.