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OMIS 105 Final questions well answered already passed
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OMIS 105 Final questions well answered already passed
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OMIS 105 FinalDynamic View - correct answer ✔✔Standard queries used in a virtual table, that is temporary, once the
query is closed it goes away
Materialized views - correct answer ✔✔create table that becomes part of the db, stored on the physical
disk, requires synchronization to refresh data
advantages of dynamic views - correct answer ✔✔-simplify query commands
- help provide data security and confidentiality
- user does not have access to all the data only those that are presented
- can also grant & revoke access
ex: one user can be granted access to see that aggregated data but does not have access to the detailed
base table
some people like creating views that are the same as the base table because views contribute to greater
programming activity as databases evolve- changes in the db means all data that refers to the db needs
to be changed whereas changed if everyone uses the view then that one view only needs to be changed
- improve programmer productivity
- contain most current base table info
- use little storage space
- provide a customized view for a user
- establish physical data independence
disadvantages of views - correct answer ✔✔-dynamic views require significant run time because the
virtual table is recreated every time the view is referenced
- dynamic views may or may not be directly updatebale
- materialized views can only improve performance if the data is relatively static and does not need to be
refreshed that often
-
, triggers - correct answer ✔✔a set of SQL statements that are triggered when a data modification (insert,
update, delete) occurs or if certain data definitions are not encountered
- if a condition is met trigger can be triggered, potential to cascade down - *more powerful than table
and column constraints, however not as efficient
significant advantage over a constraint, is it can produce a customized user message about the
occurrence of an event, constraint just produces standardized error message*
triggers can be used - correct answer ✔✔- to ensure referential integrity (if there is a foreign key in one
relation either each foreign key value must match a primary key in another relation or the foreign key
value must be null
- enforce business rules
- create audit trails
- replicate tables
- activate a procedure
3 parts to a trigger - correct answer ✔✔- event, condition, action
ex: price updates in db to be made
event: price update/change needs to be added to db
condition: for each row
action: after the event, insert specified values into PriceUpdate_t
disadvantages to triggers - correct answer ✔✔- are automatic
- can cascaded down
- if user who has access to db but not editing access can write a trigger to give himself editing access
Routines - correct answer ✔✔- collections of SQL statements that are executed when called
procedure - correct answer ✔✔a collection of procedural and SQL statements that are assigned a unique
name within the schema and stored in the db
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